Genesis 3:15 is commonly called the "Protoevangelium", meaning "The first Gospel". This is because it contains the first reference to the Messiah in the Bible - the promised seed of the woman who will "bruise the head of the serpent", who is Satan (Revelation 12:9, 20:2):
Genesis 3:15
15 And I will put enmity between thee and the woman, and between thy seed and her seed; it shall bruise thy head, and thou shalt bruise his heel.
Notice above, that the seed of the woman, Jesus Christ, will be the one to bruise the head of the serpent, while the serpent will bruise His heel - a reference to the temporary anguish of the cross. Jesus crushed the head of the serpent when He conquered death (Colossians 2:14-15, Hebrews 2:14-15: 1 John 3:8). Similarly, it is God who will crush the serpent in a final, everlasting way, under the feet of the Church (Romans 16:20), which is the Body of Christ (Ephesians 1:22-23, Colossians 1:18, 1:24).
Therefore, Genesis 3:15 is extremely valuable in establishing that God has consistently preached that He would send a Messiah to redeem mankind, starting from the very beginning. This first promise made to Adam and Eve is the basis from which all the prophets preached the same message of the Messiah which was to come (Acts 10:43, 26:22-23). And, when witnessing to Muslims and Jews, especially, the reference to the "bruising of His heel" is invaluable, because it points to something that they both reject - the crucifixion of the Messiah.
The Latin Vulgate has been the primary Bible translation used by the Catholic Church for many hundreds of years. It was so enshrined, that at the Council of Trent (1545-1563 AD), it was forbidden to be rejected "under any pretext whatsoever":
The Council of Trent - Session 4 (1546 AD)
Moreover, the same sacred and holy synod, considering that no little utility may accrue to the Church of God, if, out of all the Latin editions, now in circulation of the sacred books, it be known which is to be held as authentic, ordains and declares, that the said old and vulgate edition, which, by the long usage of so many ages, has been approved in the Church, be, in public lectures, disputations, preachings, and expositions, held as authentic; and that no one is to dare, or presume to reject it under any pretext whatsoever.
Later, Pope Pius XII (1876-1958 AD), when teaching on the issue of Bible translation, also stated that the Church taught, and continues to teach, that the Latin Vulgate is "free from any error whatsoever in matters of faith and morals":
Pope Pius XII - Divino Afflante Spiritu (1943 AD)
Hence this special authority or as they say, authenticity of the Vulgate was not affirmed by the Council particularly for critical reasons, but rather because of its legitimate use in the Churches throughout so many centuries; by which use indeed the same is shown, in the sense in which the Church has understood and understands it, to be free from any error whatsoever in matters of faith and morals; so that, as the Church herself testifies and affirms, it may be quoted safely and without fear of error in disputations, in lectures and in preaching; and so its authenticity is not specified primarily as critical, but rather as juridical.
However, in spite of the laudatory language used of the Vulgate above, the Protoevangelium in the Latin Vulgate contains an indisputable error, which alters the meaning of the text, and changes what it teaches. This error can be seen in the Douay-Rheims version of the Bible, which is a translation of the Latin Vulgate into English:
Genesis 3:15 (Douay-Rheims)
15 I will put enmities between thee and the woman, and thy seed and her seed: she shall crush thy head, and thou shalt lie in wait for her heel.
Notice that the Vulgate mistook the gender of the second clause of this sentence. The pronouns refer to the antecedent "seed", and consequently, they are rendered "he" and "his" in virtually every other translation of the Bible - emphasizing that Jesus was that singular "seed of the woman" being referred to; that "last Adam" (1 Corinthians 15:45) who was to be the representative of mankind, sent to redeem mankind - but it could also be rendered "they" and "their", if one wanted to argue that multiple descendants were in mind. In no case could it only be rendered "she" and "her".
Consequently, if all that a person had was the Latin Vulgate, they would be utterly unequipped to find the Lord Jesus in the Protoevangelium. Instead, their eyes would be turned toward Mary as having "crushed the head of the serpent", which is exactly how this passage in the Vulgate was historically applied by Roman Catholics. The Vulgate, instead of pointing toward the Lord Jesus, accelerated Mariolatry.
This is why, in Catholic statuary, it's common to see Mary depicted standing on a serpent - not so with Christ. The glory of Christ's conquering of the Devil has been taken from Him, and given to Mary, on the basis of this mistranslation.
Further, when Pope Pius IX (1792-1878 AD) defined the Immaculate Conception, as well as in the lead-up to the definition, he frequently referenced the Vulgate's erroneous rendering of the Protoevangelium, repeatedly stating that Mary crushed the head of the serpent:
Pope Pius IX - Ubi Primum (1849 AD)
4 Great indeed is Our trust in Mary. The resplendent glory of her merits, far exceeding all the choirs of angels, elevates her to the very steps of the throne of God. Her foot has crushed the head of Satan. Set up between Christ and His Church, Mary, ever lovable and full of grace, always has delivered the Christian people from their greatest calamities and from the snares and assaults of all their enemies, ever rescuing them from ruin.
Pope Pius IX - Ineffabilis Deus (1854 AD)
These ecclesiastical writers in quoting the words by which at the beginning of the world God announced his merciful remedies prepared for the regeneration of mankind - words by which he crushed the audacity of the deceitful serpent and wondrously raised up the hope of our race, saying, "I will put enmities between you and the woman, between your seed and her seed" - taught that by this divine prophecy the merciful Redeemer of mankind, Jesus Christ, the only begotten Son of God, was clearly foretold: That his most Blessed Mother, the Virgin Mary, was prophetically indicated; and, at the same time, the very enmity of both against the evil one was significantly expressed. Hence, just as Christ, the Mediator between God and man, assumed human nature, blotted the handwriting of the decree that stood against us, and fastened it triumphantly to the cross, so the most holy Virgin, united with him by a most intimate and indissoluble bond, was, with him and through him, eternally at enmity with the evil serpent, and most completely triumphed over him, and thus crushed his head with her immaculate foot.
Pope Pius IX - Ineffabilis Deus (1854 AD)
They also declared that the most glorious Virgin was Reparatrix of the first parents, the giver of life to posterity; that she was chosen before the ages, prepared for himself by the Most High, foretold by God when he said to the serpent, "I will put enmities between you and the woman." - Unmistakable evidence that she crushed the poisonous head of the serpent.
Pope Pius IX - Ineffabilis Deus (1854 AD)
All our hope do we repose in the most Blessed Virgin - in the all fair and immaculate one who has crushed the poisonous head of the most cruel serpent and brought salvation to the world
The above is an egregious misuse of Scripture, justified by appealing to a mistranslation, and it constitutes a substantial part of his argument in favor of Mary's Immaculate Conception.
This error was repeated by Pope Pius X (1835-1914 AD) in an encyclical celebrating the 50th anniversary of the definition of the Immaculate Conception:
Pope Pius X - Ad Diem Illum Laetissimum (1904 AD)
6 The Lamb that is to rule the world will be sent - but He will be sent from the rock of the desert; the flower will blossom, but it will blossom from the root of Jesse. Adam, the father of mankind, looked to Mary crushing the serpent's head, and he dried the tears that the malediction had brought into his eyes.
25 But neither will the Virgin ever cease to succor us in our trials, however grave they be, and to carry on the fight fought by her since her conception, so that every day we may repeat: "To-day the head of the serpent of old was crushed by her" (Office Immac. Con., 11. Vespers, Magnif.).
33 Oh yes, if we trust as we should in Mary, now especially when we are about to celebrate, with more than usual fervor, her Immaculate Conception, we shall recognize in her that Virgin most powerful "who with virginal foot did crush the head of the serpent" (Off. Immac. Conc.).
Above, rather than exalting Jesus Christ for conquering the Devil, the Pope exalts Mary, "who with virginal foot did crush the head of the serpent". This attributes the Lord's work to another, thereby stealing praise that rightfully belongs to Him.
Finally, note that in the 1979 revision of the Vulgate (Nova Vulgata) - the first such revision in over 380 years - the reading of the Protoevangelium was changed to "he" (ipsum), instead of the Clementine Vulgate's "her" (ipsa), bringing it in line with virtually every other Bible:
Genesis 3:15
15 Inimicitias ponam inter te et mulierem et semen tuum et semen illius ipsa conteret caput tuum et tu insidiaberis calcaneo eius. (Clementine Vulgate)
15 Inimicitias ponam inter te et mulierem et semen tuum et semen illius; ipsum conteret caput tuum, et tu conteres calcaneum eius". (Nova Vulgata)
This is a tacit admission that the Vulgate was in error, for all of that time, even though the results of that error - further Marian exaltation - remain firmly in place. Therefore, this error certainly affected doctrine, and led to errors in faith, refuting Pope Pius XII's assertion that the Vulgate was "free from any error whatsoever in matters of faith and morals".
Any person using the Latin Vulgate prior to 1979 AD would have been disabled from preaching Jesus from the Protoevangelium, because of an error that it contained. Yet, the Council of Trent ruled that no one may "presume to reject it under any pretext whatsoever".
This is an instance where dogmatism absolutely affects doctrine, one's ability to learn, and one's ability to get the truth from God's Word, because of the enshrining of the work of very fallible sinners. If the Catholic Church was indisputably wrong to rule that none could reject their errant (see Appendix II for other examples of errors), fallible Vulgate "under any pretext whatsoever", why should we take their other claims of authority seriously?
While the Council of Trent (1545-1563 AD) established the Vulgate as authoritative, it did not specify which edition of the Vulgate was to be regarded as the standard version.
As a result, Pope Sixtus V (1520-1590 AD) took it upon himself to issue his own edition of Vulgate in 1590 AD, which he defined to be the authoritative version mentioned in Trent, despite, obviously, the fact that it didn't even exist until over 25 years after the Council of Trent concluded. This Sixtine Vulgate, as it is called, was published with the Papal Bull Aeternus Ille affixed to the introduction, which says:
Pope Sixtus V - Aeternus Ille (1590 AD)
To the praise and glory of Almighty God, for the preservation and increase of the Catholic faith, and the utility of the holy universal Church, by this our constitution, which is to remain in force forever, with the counsel and assent of our venerable brethren the Cardinals of the holy Roman Church, appointed over the Vatican printing house, whose work and diligence we used in the more serious matters of this correction of the Vulgate edition, and from our certain knowledge and the fullness of Apostolic power, we decree and declare that the Vulgate Latin edition of the sacred pages, both old and new Testament, which was received as authentic by the Council of Trent, is to be considered without any doubt or controversy as the very one which, corrected as well as possible and printed in the Vatican printing house, we now publish to be read in the entire Christian Republic and in all the Churches of the Christian world, decreeing that it is confirmed, first by the universal consent of the holy Church and the holy Fathers, then by the decree of the General Council of Trent, and now also by the Apostolic authority handed down to us by the Lord, as the true, legitimate, authentic, and undoubted one, to be received and held in all public and private disputations, readings, sermons, and expositions.
In the above Bull, Pope Sixtus is declaring his revision to be the standard "without any doubt or controversy". He died a few months after the first printing, which has been scanned and uploaded to the Internet Archive, where anyone can see the Bull cited above to be authorized by Pope Sixtus, and published in the Bible itself.
However, after the death of Pope Sixtus, the Church hurriedly rejected his edition of the Vulgate. The Church suspended sale of it 9 days after he died, and his successor, Pope Clement VIII (1536-1605 AD), ordered Pope Sixtus V's edition of the Vulgate to be recalled in 1592 AD - two years after it was published. Pope Clement VIII then revised it, and his version, called the Sixto-Clementine Vulgate, is what would be used until 1979 AD.
So, the Council of Trent declared that the Vulgate was to be held as authentic, but failed to define the authoritative edition, leading to a later Pope publishing his own edition as the authoritative version, even though that was swiftly rejected and discarded after he died. Then, another Pope would further revise it, and that further revision would become the accepted edition for the next 380 years.
Therefore, no one can reject the text "under any pretext whatsoever", even though no one was sure what that text was even supposed to be, and the first attempt to canonize a standard edition was universally regarded to be a failure, even though the "Vicar of Christ" who was making the attempt declared it to be the authoritative standard at the time.
Below demonstrates other errors in the Clementine Vulgate, which is "free from any error whatsoever in matters of faith and morals" (Pope Pius XII, Divino Afflante Spiritu).
Below will show the verse in the Clementine Vulgate, the Douay-Rheims, which is an English translation of the Clementine Vulgate, and the Nova Vulgata, which is the official revision of the Clementine Vulgate published in 1979. There is no official English translation of the Nova Vulgata, but the NABRE will be used, as it is an approved Catholic translation of the Bible.
1 Samuel 13:1
1 Saul was a child of one year when he began to reign, and he reigned two years over Israel. (Douay-Rheims)
1 Saul was... years old when he became king and he reigned...[two years] over Israel. (NABRE)
1 Filius unius anni Saul cum regnare coepisset duobus autem annis regnavit super Israhel. (Clementine Vulgate)
1 Filius annorum Saul, cum regnare coepisset; duobus autem annis regnavit super Israel. (Nova Vulgata)
Saul was not a "child of one year when he began to reign". Rather, he was a "young man" who was a head taller than all the people of Israel (1 Samuel 9:2).
John 3:5
5 Jesus answered: Amen, amen, I say to thee, unless a man be born again of water and the Holy Ghost, he cannot enter into the kingdom of God. (Douay-Rheims)
5 Jesus answered, "Amen, amen, I say to you, no one can enter the kingdom of God without being born of water and Spirit. (NABRE)
5 Respondit Iesus amen amen dico tibi nisi quis renatus fuerit ex aqua et Spiritu non potest introire in regnum Dei (Clementine Vulgate)
5 Respondit Iesus: "Amen, amen dico tibi: Nisi quis natus fuerit ex aqua et Spiritu, non potest introire in regnum Dei. (Nova Vulgata)
The Vulgate errantly read "born again of water", when in the original Greek, it simply says "born of water".
This misrendering accommodates the doctrine of Baptismal Regeneration, and affects the meaning of the verse.
1 Corinthians 15:51
51 Behold, I tell you a mystery. We shall all indeed rise again: but we shall not all be changed. (Douay-Rheims)
51 Behold, I tell you a mystery. We shall not all fall asleep, but we will all be changed, (NABRE)
51 Ecce mysterium vobis dico omnes quidem resurgemus sed non omnes inmutabimur. (Clementine Vulgate)
51 Ecce mysterium vobis dico: Non omnes quidem dormiemus, sed omnes immutabimur, (Nova Vulgata)
The Clementine Vulgate had a very errant reading for the second part of the verse. "We shall not all fall asleep" is made to say "We shall all indeed rise again", and "but we will all be changed" is made to say "but we shall not all be changed".
Hebrews 11:21
21 By faith Jacob, dying, blessed each of the sons of Joseph and adored the top of his rod. (Douay-Rheims)
21 By faith Jacob, when dying, blessed each of the sons of Joseph and "bowed in worship, leaning on the top of his staff." (NABRE)
21 Fide Iacob moriens singulis filiorum Ioseph benedixit et adoravit fastigium virgae eius. (Clementine Vulgate)
21 Fide Iacob moriens singulis filiorum Ioseph benedixit et adoravit super fastigium virgae suae. (Nova Vulgata)
The Clementine Vulgate literally says Jacob "worshipped the top of his staff", and it is rendered as such in the Douay-Rheims.