For Christ also suffered once for sins, the righteous for the unrighteous, that he might bring us to God, being put to death in the flesh but made alive in the spirit, in which he went and proclaimed to the spirits in prison, because they formerly did not obey, when God's patience waited in the days of Noah, while the ark was being prepared, in which a few, that is, eight persons, were brought safely through water. Baptism, which corresponds to this, now saves you, not as a removal of dirt from the body but as an appeal to God for a good conscience, through the resurrection of Jesus Christ, who has gone into heaven and is at the right hand of God, with angels, authorities, and powers having been subjected to him. (1 Pet. 3:18-22)
The first half of that is confusing and unclear what it means. I've left it in for context. It's the latter half--vv. 21-22--that's significant. While Peter says "baptism ... now saves you," he goes on to say it's
not the physical act, but what it represents: an appeal to God.
Like communion, baptism is a sacrament--properly understood, a symbol or sign. It represents something else. The
sign is the physical washing of the body. The
thing signified is the washing of the spirit by the blood of Christ. Baptismal regenerationists, such as Roman Catholics, Lutherans or Campbellites, confuse symbol and substance.
But it
is a big deal, because Christ commanded it. It is not a necessity for salvation, but it is a necessity for obedience. If the regenerationists conflate the symbol and the substance, people who say baptism is no big deal (implying it's something entirely optional) divorce them. If baptism is the sign of that good conscience before God, then the Christian ought to embrace it as a testimony to what God has worked in him. But leave the credit to Christ for the saving work that he has accomplished; don't credit it to the water.