"For David did not ascend to heaven, and yet he said, “‘The Lord said to my Lord: “Sit at my right hand until I make your enemies a footstool for your feet.”’ (Acts 2:34-35)Here Peter is talking to the locals in Jerusalem who had just crucified Jesus before He raised from the dead and ascended to Heaven. These Jews revered David and He was their greatest King up to that point. But now Peter saying that there's a better king, an eternal king because after all, David didn't rise from the dead and go sit at the right hand of the Father like Jesus did. In fact, David prophesied about a time when God the Father spoke to the Son, Jesus, telling Him to sit at His right hand. And in this quote from the Psalms, David refers to Jesus as His lord. Peter wants the people to see that David prophesied about the majesty of Jesus. Even a thousand years before Jesus was born. David knew that He is where the joy is!