Then why does Peter even mention water if water kills and does not save?
Because Peter is using a symbolism.
Why did Jesus command water baptism if it kills and does not save?
Jesus answered, "Truly, truly, I say to you, unless one is born of water and the Spirit he cannot enter into the kingdom of God.
He was saying that Nicodemus and the ones with him had been born from his mother. Unless one is born into this world, there is no way one can be born of the Spirit.
We are born dead into this world. Jesus was talking about spiritual things, not physical things.
I mean, even Nicodemus understood that Jesus was talking about being born of his mother ("How can someone be born when they are old?" Nicodemus asked. "
Surely they cannot enter a second time into their mother's womb to be born!")
Why do we see water and the Spirit in conversions? Why do conversions end in baptism?
39When they came up out of the water, the Spirit of the Lord snatched Philip away; and the eunuch no longer saw him, but went on his way rejoicing.
There, see it, you said so yourself. Conversions
end in water baptism.
Conversions do not begin in water baptism, it END in water baptism.
The eunuch was
already saved
before he got wet.
Not the other way around.
The water did not save the eunuch, the eunuch was saved because the eunuch believed the salvation that Jesus Christ and what He did at the Cross of Calvary affords.