"For Christ also died for sins once for all, the just for the unjust, so that He might bring us to God, having been put to death in the flesh, but made alive in the spirit; in which also He went and made proclamation to the spirits now in prison, who once were disobedient, when the patience of God kept waiting in the days of Noah, during the construction of the ark, in which a few, that is, eight persons, were brought safely through the water. Corresponding to that, baptism now saves you---not the removal of dirt from the flesh, but an appeal to God for a good conscience---through the resurrection of Jesus Christ, who is at the right hand of God, having gone into heaven, after angels and authorities and powers had been subjected to Him" (1 Peter 3:18-22, NASB).
I have read a thought-provoking sermon by evangelical Baptist theologian and author John Piper called, "Strengthened to Suffer: Christ, Noah, and Baptism." You may read the entire sermon at http://www.desiringgod.org/ResourceLibrary/Sermons/ByTopic/23/884_Strengthened.
Here is a portion of his sermon:
Verse 18 said that Christ died for sins and brought us to God. In other words Christ saves us. But the question is: who is us? Whom does Christ's death actually save? That's what verse 21 answers: those who are baptized. But Peter knows that this will be misunderstood if he does not qualify it. So when he says, "Baptism now saves you," he adds, "Not the removal of dirt from the flesh, but an appeal to God for a good conscience." This is virtually a definition of baptism. Baptism is an outward expression of a spiritual, inward appeal to God for cleansing. In other words, baptism is a way of saying to God: "I trust you to apply the death of Jesus to me for my sins and to bring me through death and judgment into new and everlasting life through the resurrection of Jesus."
Baptism may cleanse the body because it was by immersion. But that is not why he says it saves. It saves for one reason: it is an expression of faith. It is an appeal of faith. Paul said in Romans 10:13 that whoever calls upon the name of the Lord shall be saved. Baptism is such a calling. It is an appeal to the Lord.
How does this strengthen us for suffering with Christ?
Like this: When we have come through the water of baptism, we have passed through death and judgment. We have been buried with Christ and we have risen with him. We have passed from death to life. Judgment is past. The suffering we are experiencing cannot be the condemnation of God. That has already been experienced for us by Christ. We have received that by faith and we have expressed our faith in baptism. It stands as a constant reminder that the worst suffering has been averted. Christ took it for us. We will never have to come into judgment. There is now no condemnation. We have already died that death in Christ and been raised in him. Therefore our present suffering is not the wrath of God but the loving discipline of our Father and the preparation for glory.