this saving baptism is not water here but a spiritual one where our inner man is risen with Chris and because of the full assurance we have in our conscience now by the resurrection of Jesus.
The key to 1 Peter 3:21 is the word the answer (or inquiry) of a good conscience. The word "conscience is very important here.
We see in hebrews 9 more about the conscience.
"Which was a figure for the time then present, in which were offered both gifts and sacrifices, that could not make him that did the service perfect, as pertaining to the conscience; 10 Which stood only in meats and drinks, and divers washings, and carnal ordinances, imposed on them until the time of reformation.:" ( Hebrews 9L9,10 KJV)
Notice here that the conscience cannot be perfect or clean or good by the outward diverse washings (the word washing there is a word used for baptism in greek I believe, ). The conscience comes from two words con ( with0 science ( knowledge, so with knowledge. They did not have the full knowledge of Christ finished work or the full assurance, so their hearts could be pure and right in faith but their conscience could not. But the way to have a clean conscience is defined here also,
“How much more shall the blood of Christ, who through the eternal Spirit offered himself without spot to God, purge your conscience from dead works to serve the living God?” (Hebrews 9:14 KJV)
So when Peter says the saving baptism is the answer of a good conscience by the resurrection of Jesus Christ. This refers to our inner man and witness and a spiritual assurance by faith because of Jesus resurrection and our being risen with him. In the ark of Noah was a type of being in Christ raised up into the heavenlies to a new world where we are at rest in Christ,Noah's name meaning rest.
The one saving baptism is this
“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.” (1 Cor 12:13 KJV)
“For as many of you as have been baptized into Christ have put on Christ.” (Galatians 3:27 KJV) this is not to be dunked under water and put on water. But to be immersed into Christ by the Spirit and we put on Christ and are in him and he is us.
“Know ye not, that so many of us as were baptized into Jesus Christ were baptized into his death?” (Romans 6:3 KJV) Notice that the baptism (immersion) is into Jesus Christ, not into water.
To be immersed ( baptized into Christ and to put on Christ is the saving baptism. This is not water baptism of John. Even the apostles were s till under the law all through acts following the Ot law and customs and diverse washings and carnal ordinances and Peter was still following Johns water baptism when he baptized the gentiles in Acts and read chapter 11 of he remembered thee words of jesus in Acts 1 how that John baptized ( past tense) with \water, but they would be baptized with the Spirit .
Also the Jewish and Gentile issue is all over the New testament. The book of acts we see the reformation from the old to the New and the transition is clear. But many Jewish believers were still struggling and under the law zealous of it and the temple many years after Christ death, read Acts 21 when Paul went to Jerusalem and James told him how many Jewish believers in jesus there were who were all zealous of the law and customs and they even did an animal sacrifice .