Christians who teach that a Christian must be obedient to God in order to be saved from Hell (or "prove they are saved", which is a semantic way to arrive at the same outcome), are teaching that a Christian must keep the Law to be saved.
This article will prove that this is what they are teaching, discuss why it's not true, and why our obedience never has anything to do with our justification before God, according to the Bible.
The Law is the standard by which "sin" is defined, because sin, by definition, is breaking the Law:
Romans 7:7
7 What shall we say then? Is the law sin? God forbid. Nay, I had not known sin, but by the law: for I had not known lust, except the law had said, Thou shalt not covet.
1 John 3:4
4 Whosoever committeth sin transgresseth also the law: for sin is the transgression of the law.
Therefore, since all sin breaks the Law, keeping the Law would require being sinlessly perfect. As a corollary, any commandment to avoid any sin is a commandment to keep the Law.
This can further be demonstrated by the fact that "sin" is said to include anything unrighteous:
1 John 5:17
17 All unrighteousness is sin: and there is a sin not unto death.
Since "all unrighteousness is sin", and "sin is the transgression of the Law", that means that anything that can be called "unrighteous" is also a violation of the Law.
We get further insight into what the Law entails by looking at the words of Jesus Christ, when He said:
Matthew 22:37-40
37 Jesus said unto him, Thou shalt love the Lord thy God with all thy heart, and with all thy soul, and with all thy mind.
38 This is the first and great commandment.
39 And the second is like unto it, Thou shalt love thy neighbour as thyself.
40 On these two commandments hang all the law and the prophets.
Here, Jesus summarizes the Law into two great commandments - loving God and neighbor entirely - both of which are direct quotations from the Old Testament (Deuteronomy 6:5, Leviticus 19:18). The Law, then, encompasses any good thing that you do, whether for others or for God.
Elsewhere, Jesus further distilled the Law into a single commandment:
Matthew 7:12
12 Therefore all things whatsoever ye would that men should do to you, do ye even so to them: for this is the law and the prophets.
Once again, anything conceivably "good" that you can do falls under the above verse, of which Jesus says encapsulates the entire Law.
These passages are sufficient to show that doing any good deed, along with any avoidance of performing any bad deed, falls under the scope of the Law, according to the Word of God.
The Bible is clear that everyone has broken the Law of God. Recall that "sin is the transgression of the Law":
Romans 3:23
23 For all have sinned, and come short of the glory of God;
Since all have sinned, all have broken the Law. Other verses that teach that everyone on earth has sinned at some point in the past are 1 John 1:10, Romans 5:12, and Galatians 3:22.
However, the fact that you sin is an ongoing situation. No one has stopped sinning, and no one in their daily life lives free from sin:
1 John 1:8
8 If we say that we have no sin, we deceive ourselves, and the truth is not in us.
Recall that "all unrighteousness is sin":
Romans 3:10-12
10 As it is written, There is none righteous, no, not one:
11 There is none that understandeth, there is none that seeketh after God.
12 They are all gone out of the way, they are together become unprofitable; there is none that doeth good, no, not one.
Other verses that teach that all people sin on a continual basis are Ecclesiastes 7:20, Psalm 14:2-3, and 1 Kings 8:46.
Furthermore, if you have ever broken any aspect of the Law, you are put into the same category by God as someone who has broken any other aspect of the Law - you're both lawbreakers:
James 2:9-11
9 But if ye have respect to persons, ye commit sin, and are convinced of the law as transgressors.
10 For whosoever shall keep the whole law, and yet offend in one point, he is guilty of all.
11 For he that said, Do not commit adultery, said also, Do not kill. Now if thou commit no adultery, yet if thou kill, thou art become a transgressor of the law.
Therefore, no one can say that they "keep the Law", even in part, because the Law cannot be kept in part. It can only be kept completely, or it has been violated.
Because everyone violates the Law, the Scripture states that none can be justified by the Law in the sight of God:
Romans 3:20
20 Therefore by the deeds of the law there shall no flesh be justified in his sight: for by the law is the knowledge of sin.
Galatians 3:11
11 But that no man is justified by the law in the sight of God, it is evident: for, The just shall live by faith.
Therefore, because no one is justified by the Law in God's sight, and the Law contains any conceivably good thing that one could possibly do, "good behavior" has nothing whatsoever to do with our justification before God, at any point in time.
This is because the standard by which everyone will be judged after death is the Law, in comparison to Jesus Christ:
Acts 17:31
31 Because he hath appointed a day, in the which he will judge the world in righteousness by that man whom he hath ordained; whereof he hath given assurance unto all men, in that he hath raised him from the dead.
The above verse shows that you will be judged by the Law, because it is the standard by which "righteousness" is defined. It says that you will be judged against Jesus, who never broke the Law (2 Corinthians 5:21, Hebrews 4:15: 1 Peter 2:21-22: 1 John 3:5). Since all have sinned, all will fail this judgement, which is why none can be justified by the Law.
Why then did God give a Law which no one could keep, and that no one can be justified by?
The Law was given to reveal to us our sinful condition before God, and to emphasize to us our need for a Savior:
Romans 3:19-20
19 Now we know that what things soever the law saith, it saith to them who are under the law: that every mouth may be stopped, and all the world may become guilty before God.
20 Therefore by the deeds of the law there shall no flesh be justified in his sight: for by the law is the knowledge of sin.
Galatians 3:19, 24
19 Wherefore then serveth the law? It was added because of transgressions, till the seed should come to whom the promise was made; and it was ordained by angels in the hand of a mediator.
24 Wherefore the law was our schoolmaster to bring us unto Christ, that we might be justified by faith.
That's the point of the Law. It reveals how drastically inferior you are in comparison to what God expects and demands, which drives any honest person towards Jesus Christ for justification.
We are only reckoned as righteous before God by faith alone based on the merits of Christ, not our own imperfect, futile attempts to keep the Law.
The following passages teach this clearly:
Galatians 2:16
16 Knowing that a man is not justified by the works of the law, but by the faith of Jesus Christ, even we have believed in Jesus Christ, that we might be justified by the faith of Christ, and not by the works of the law: for by the works of the law shall no flesh be justified.
Romans 10:4
4 For Christ is the end of the law for righteousness to every one that believeth.
Acts 13:39
39 And by him all that believe are justified from all things, from which ye could not be justified by the law of Moses.
Romans 3:21-22, 28
21 But now the righteousness of God without the law is manifested, being witnessed by the law and the prophets;
22 Even the righteousness of God which is by faith of Jesus Christ unto all and upon all them that believe: for there is no difference:
28 Therefore we conclude that a man is justified by faith without the deeds of the law.
Romans 9:31-32
31 But Israel, which followed after the law of righteousness, hath not attained to the law of righteousness.
32 Wherefore? Because they sought it not by faith, but as it were by the works of the law. For they stumbled at that stumblingstone;
Philippians 3:9
9 And be found in him, not having mine own righteousness, which is of the law, but that which is through the faith of Christ, the righteousness which is of God by faith:
Notice that all of the verses above explicitly say that we are justified by faith to the exclusion of the Law. There is no mixing of the concepts, because they are diametrically opposed.
That also means that "faith" cannot be redefined to include obedience to the Law - which as the first part of this article showed, includes any good thing that a person may do. Faith is simple belief in Jesus Christ for Salvation from Hell, excluding all works (Ephesians 2:8-9, Romans 4:5, Titus 3:5).
If someone mandates that any obedience to God is required for getting to Heaven, then they are essentially saying that Jesus died for no reason, to save nobody from anything:
Galatians 2:21
21 I do not frustrate the grace of God: for if righteousness come by the law, then Christ is dead in vain.
Notice above that imputed righteousness (Romans 4:6-8) apart from the Law is described as "grace", which by definition, excludes any and all work (Romans 11:6).
If, in spite of the above, you try to add Law-keeping in addition to faith for justification, you nullify justification by faith entirely, and must keep the entire Law perfectly:
Galatians 3:10
10 For as many as are of the works of the law are under the curse: for it is written, Cursed is every one that continueth not in all things which are written in the book of the law to do them.
Galatians 5:1-5
1 Stand fast therefore in the liberty wherewith Christ hath made us free, and be not entangled again with the yoke of bondage.
2 Behold, I Paul say unto you, that if ye be circumcised, Christ shall profit you nothing.
3 For I testify again to every man that is circumcised, that he is a debtor to do the whole law.
4 Christ is become of no effect unto you, whosoever of you are justified by the law; ye are fallen from grace.
5 For we through the Spirit wait for the hope of righteousness by faith.
The above passages demonstrate that if any obedience to the Law was required to Salvation, perfect obedience would be required. This is because, as already seen, if you break the Law in a single aspect, you are as condemned as someone who has broken it in every aspect (James 2:10).
This mixing of faith and Law-keeping for Salvation is explicitly condemned in Acts chapter 15:
Acts 15:1, 5-11
1 And certain men which came down from Judaea taught the brethren, and said, Except ye be circumcised after the manner of Moses, ye cannot be saved.
5 But there rose up certain of the sect of the Pharisees which believed, saying, That it was needful to circumcise them, and to command them to keep the law of Moses.
6 And the apostles and elders came together for to consider of this matter.
7 And when there had been much disputing, Peter rose up, and said unto them, Men and brethren, ye know how that a good while ago God made choice among us, that the Gentiles by my mouth should hear the word of the gospel, and believe.
8 And God, which knoweth the hearts, bare them witness, giving them the Holy Ghost, even as he did unto us;
9 And put no difference between us and them, purifying their hearts by faith.
10 Now therefore why tempt ye God, to put a yoke upon the neck of the disciples, which neither our fathers nor we were able to bear?
11 But we believe that through the grace of the Lord Jesus Christ we shall be saved, even as they.
We see from the above that almost as soon as the early church began, there were self-righteous people teaching others that they had to keep the Law in addition to belief to be saved, trying to rob them of grace, and a proper and total trust in Jesus Christ. Common sense says that if obedience to the Law is mandated for Salvation, your faith has to be in yourself, to save yourself, since you have to perform.
So, not only are we saved by faith, we are saved by faith explicitly without the Law, that is, without doing good things, or avoiding doing bad things. This proves that no room is left for anything to be added to faith for Salvation, provided you understand the scope of the Law.
In summary, the Bible teaches that:
Therefore, anyone teaching that obedience to Jesus Christ somehow plays a role in you going to Heaven is a false prophet. They are teaching the Legalism that is warned about over and over again in the New Testament, even if they don't understand or admit that they are teaching the Law.
Such false prophets do not understand the scope or purpose of the Law, nor do they understand what would be required if justification by the Law was actually necessary.