“Let all the house of Israel therefore know for certain that God has made him both Lord and Christ, this Jesus whom you crucified" (v36). Speaking to the crowd of international Jews, Peter referenced King David and his prophecies about a coming mighty ruler for Israel (v25-35); this “Lord and Christ” was the resurrected Jesus. When the crowds repented and believed in Jesus, they immediately began living in obedience to their new King: sharing their possessions, learning, worshipping, praying, and spending time together (v42).
“Repent and be baptized … in the name of Jesus” (v38). “Repent” means to “turn away” from our old loyalties, by faith choosing to honor Jesus as the King of our souls.