Baptismal Regeneration is the doctrine that water baptism grants the remission of sins, the new birth, the indwelling of the Holy Spirit, and entrance into the Body of Christ. For those who believe in the doctrine of Original Sin, water baptism is also seen as the ordinary way to cleanse a child of Original Sin.
Nearly every denomination which teaches Baptismal Regeneration also teaches that a believer can lose their Salvation. If water baptism is when a person receives the new birth, how can that person go to Hell?
Either:
If the second option is true, how does one get born again, again? None of these groups re-baptize. If their assertion is that water baptism grants the new birth, why don't they re-baptize after apostasy, or major sins?
The Bible teaches that the new birth is "born of incorruptible seed" (1 Peter 1:23), an entirely new creation (2 Corinthians 5:17), utterly without sin (1 John 3:9, 5:18), and a sibling of Jesus Christ (Romans 8:29). How could such a being go to Hell?
Baptismal Regenerationalists demolish the entire doctrine of the new birth, firstly by tying it to water baptism, but also because they teach almost uniformly that a person who is born again can ultimately go to Hell.
Notice how in First Corinthians, the Apostle Paul explicitly separates baptism from the Gospel:
1 Corinthians 1:17
17 For Christ sent me not to baptize, but to preach the gospel: not with wisdom of words, lest the cross of Christ should be made of none effect.
When the Apostle Paul expounds the Gospel message later in the same book, water baptism is conspicuously absent (1 Corinthians 15:1-8).
So, Paul was not sent to baptize people, and what he was preaching, the Gospel message, does not include baptism. Yet this Gospel message is said to be the power of God that leads a person to faith in Jesus, immortality, and Salvation:
2 Timothy 1:10
10 But is now made manifest by the appearing of our Saviour Jesus Christ, who hath abolished death, and hath brought life and immortality to light through the gospel:
Romans 1:16
16 For I am not ashamed of the gospel of Christ: for it is the power of God unto salvation to every one that believeth; to the Jew first, and also to the Greek.
The above passages make perfect sense in light of the doctrine of Salvation by faith alone (John 6:47, etc.). However, they do not make sense if, despite believing in Jesus Christ, one will go to Hell unless they are water baptized.
The Bible teaches that when a person believes in Jesus, they are sealed with the Holy Spirit:
Ephesians 1:12-14
12 That we should be to the praise of his glory, who first trusted in Christ.
13 In whom ye also trusted, after that ye heard the word of truth, the gospel of your salvation: in whom also after that ye believed, ye were sealed with that holy Spirit of promise,
14 Which is the earnest of our inheritance until the redemption of the purchased possession, unto the praise of his glory.
John 7:38-39
38 He that believeth on me, as the scripture hath said, out of his belly shall flow rivers of living water.
39 (But this spake he of the Spirit, which they that believe on him should receive: for the Holy Ghost was not yet given; because that Jesus was not yet glorified.)
Galatians 3:2
2 This only would I learn of you, Received ye the Spirit by the works of the law, or by the hearing of faith?
Galatians 3:14
14 That the blessing of Abraham might come on the Gentiles through Jesus Christ; that we might receive the promise of the Spirit through faith.
The above passages argue against the Baptismal Regenerationalist assertion that the indwelling of the Holy Spirit is received at water baptism, as if that were required, all of the above would be omitting the most essential detail, and leaving a distinctly false impression.
However, beyond these statements, we also have an instance in the book of Acts where people are indwelt by the Holy Spirit, explicitly without water baptism:
Acts 10:43-44, 47
43 To him give all the prophets witness, that through his name whosoever believeth in him shall receive remission of sins.
44 While Peter yet spake these words, the Holy Ghost fell on all them which heard the word.
47 Can any man forbid water, that these should not be baptized, which have received the Holy Ghost as well as we?
Above, we see the "remission of sins", and the indwelling of the Holy Spirit, without water baptism.
Throughout the New Testament, being indwelt by the Holy Spirit stands as an identifier of the saints (Romans 5:5, 8:9, Ephesians 4:30: 1 Corinthians 3:16: 2 Corinthians 1:21-22, 5:5: 2 Timothy 1:14). Therefore, these unbaptized saints in Acts 10 refute Baptismal Regeneration.
Also contrary to the claims of most Baptismal Regenerationalists, this indwelling is a permanent operation. Ephesians 1:14 says that we are sealed "until the redemption of the purchased possession". This includes our bodies (1 Corinthians 6:19-20), which won't be redeemed until after we die (Romans 8:23). Therefore, believers are sealed for their entire lives.
This final point emphasizes the vital fact that water baptism is simply a symbol of a spiritual operation that takes place at the moment of faith.
There is "one baptism" that places a person into the body of Christ:
Ephesians 4:4-5
4 There is one body, and one Spirit, even as ye are called in one hope of your calling;
5 One Lord, one faith, one baptism,
Baptismal Regenerationalists read "water" into the above passage. It does not say "water", it says "baptism". The word "baptism" is elsewhere used euphemism for physical death (Matthew 20:22-23, Mark 10:38-39, Luke 12:50), and when used to refer to the "baptism of the Spirit", it is even contrasted with a water baptism (Matthew 3:11, Mark 1:8, Luke 3:16, Acts 1:5). It is an error to read "water" into every passage mentioning "baptism".
By comparing Scripture with Scripture, we can see that the "one baptism" mentioned above is a spiritual baptism, whereby one is placed in the body of Christ:
1 Corinthians 12:13
13 For by one Spirit are we all baptized into one body, whether we be Jews or Gentiles, whether we be bond or free; and have been all made to drink into one Spirit.
The above, in turn, refers to the indwelling of the Holy Ghost, received at the moment of faith, as discussed at length in the previous section. That is the "one baptism" that God sees. Our water baptism is merely a symbol of our being placed into the body of Christ.
It is an error to take a symbol, and turn it into the operation that it was intended to picture. It is just as erroneous as the taking of the symbol of the Lord's Supper, and ascribing to it some Salvific benefit that only the actual death of Christ achieved.
Being water baptized is an important first step of obedience for a new believer, yet mandating it for Salvation is not only a violation of all the verses discussed above, but also all those which teach that a person is not saved by works. In certain nations throughout history - including the Muslim world today, which has the death penalty for apostasy - being water baptized could lead to persecution, violence, ostracization, and death. It is a public testimony, which takes courage. Mandating it for Eternal Life is teaching works Salvation.
The fact that 80%+ of professing Christians belong to denominations which teach Baptismal Regeneration is proof positive that the way is narrow (Matthew 7:13-14). It does not matter how many hold to a doctrine, if it is errant - and this one certainly is - it needs to be rejected.