There is frequently a great misunderstanding of that passage in 1 Peter 3:19-21. So we need to look at it very closely:
By which also he [Christ] went and preached unto the spirits in prison; Which sometime were disobedient, when once the longsuffering of God waited in the days of Noah, while the ark was a preparing, wherein few, that is, eight souls were saved by water. The like figure whereunto even baptism doth also now save us (not the putting away of the filth of the flesh, but the answer of a good conscience toward God,) by the resurrection of Jesus Christ:
We need to spiritually discern what is being taught in this passage. Therefore we need to ask ourselves several questions:
1. According to the Gospel are souls saved by water or any other means, or are souls saved by repenting and believing on the Lord Jesus Christ? And the answer is obvious.
2. If that is true, in what sense does baptism "now save us"?
3. Can "eight were souls saved by water" be stated as "eight souls were saved through water"? And that is exactly what "dia" means, and should have been translated thus.
Strong's Concordance
dia: through, on account of, because of
Original Word: διά
Part of Speech: Preposition
Transliteration: dia
Phonetic Spelling: (dee-ah')
Definition: through, on account of, because of
Usage: (a) gen: through, throughout, by the instrumentality of, (b) acc: through, on account of, by reason of, for the sake of, because of.
Therefore eight souls were saved THROUGH water when the Ark went through the Deluge. There was intense rain, which means that the Ark and its occupants were figuratively "baptized" in water. And the Ark floated on the water for one year, so that too was eight souls being saved through water. Thus "the like figure (Gk antitupon = antitype)" of Christian baptism by immersion.
So now we need to determine how Christian baptism "saves us"? Is that a figure of speech or can water save anyone?
The key to the answer is in the resurrection of Jesus Christ. And that is what Peter is saying. The Bible says that Christ was raised from the dead for our justification. In other words, had Christ simply died for our sins and remained dead, it would have availed nothing. His resurrection was imperative to establish that Christ had destroyed the power of, and the penalty for sins -- destroyed the power of sin, Hades, Hell, death, and Satan. Thus He was declared "Lord" after His resurrection.
Those who believe with their hearts that Christ died for their sins and was raised for their justification are saved by grace through faith, justified by God, and forgiven of all their sins. That produces a "good conscience". Therefore when they are baptized as believers, they are telling the world that they have been saved by grace (not by the water of baptism).
Peter also makes it clear that water can only "put away" or cleanse "the flesh" (the body). So water is only good for bathing, not salvation.