Before Jesus began His ministry, you had for many years, = John the Baptist telling the unsaved Jews..
"repent and be baptized "
So, that is John The Baptist's message for the Jews..
Peter, being a Jew, told Jews the same during PENTECOST ......as at that time, The Cross had Just birthed Christianity, and the time of the gentiles had just begun.
So, Peter was preaching "the Baptist's" water message to the Jews, who were in Jerusalem, during "pentecost".
On that day, Peter nor those in the Upper room, were water baptized, yet they all spoke with "tongues".
Peter had received the Holy Spirit, before Pentecost, .. .in John 20:22, and he was not water baptized, and he didnt "speak in tongues".
15 Yrs after Jesus was BACK IN HEAVEN.. .Peter met Paul, Acts 15.... and Paul taught Peter, the "Gospel of the Grace of God".. that is..
"The preaching of the CROSS, is the Power of God, unto Salvation"...
That's not repent and get wet..