Here is the text:
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 . . .And here are Piper's words on it:
-- 1 Peter 3:21
In verse 19, Peter reminds the readers that, in the spirit, Jesus had gone to preach to the people in Noah's day, whose spirits are now in prison awaiting judgment. (I don't take the position that verse 19 refers to Jesus' preaching in hell between Good Friday and Easter.) But there was tremendous evil and hardness in Noah's day and only eight people enter the ark for salvation from the judgment through water.
Now Peter sees a comparison between the waters of the flood and the waters of baptism. Verse 21 is the key verse: "And corresponding to that [the water of the flood], 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." Now there are some denominations that love this verse because it seems at first to support the view called "baptismal regeneration." That is, baptism does something to the candidate: it saves by bringing about new birth. So, for example, one of the baptismal liturgies for infants says, "Seeing now, dearly beloved brethren, that this child is regenerate, and grafted into the body of Christ's Church, let us give thanks."
Now the problem with this is that Peter seems very aware that his words are open to dangerous misuse. This is why, as soon as they are out of his mouth, as it were, he qualifies them lest we take them the wrong way. In verse 21 he does say, "Baptism now saves you" - that sounds like the water has a saving effect in and of itself apart from faith. He knows that is what it sounds like and so he adds immediately, "Not the removal of dirt from the flesh, but an appeal to God for a good conscience - through the resurrection of Jesus Christ." (Or your version might have: "the pledge of a good conscience toward God").
But the point seems to be this: When I speak of baptism saving, Peter says, I don't mean that the water, immersing the body and cleansing the flesh, is of any saving effect; what I mean is that, insofar as baptism is "an appeal to God for a good conscience," (or is "a pledge of a good conscience toward God"), it saves. Paul said in Romans 10:13, "Everyone who calls on the name of the Lord - everyone who appeals to the Lord - will be saved." Paul does not mean that faith alone fails to save. He means that faith calls on God. That's what faith does. Now Peter is saying, "Baptism is the God-ordained, symbolic expression of that call to God. It is an appeal to God - either in the form of repentance or in the form of commitment."