Just one quick comment. The "by one Spirit" as per the KJV in 1 Cor 12:13, is a poor translation even though I personally like and read the KJV, but look at the original Greek in the interlinear, which says "in one Spirit". It does make a difference as some tend to use the KJV there to justify that somehow you receive the spirit prior to baptism, which is not the case as noted on Acts 2:38.
Acts 2:38 “what must WE do” is not even about salvation. It is a national repentance of Israel because they crucified their Messiah. Much different than the question, what must I do to be saved.