Even though the Jewish people killed their Messiah, why did this not thwart God?
Their killing of the Messiah did not thwart God because God raised Him from the dead. Death could not hold Him, for He was God. God called Him back to heaven, where He remains alive, ready to return, and still able to give them the Kingdom.
Les explains that Peter was making the point that even though they had killed their King and Messiah, they did not thwart God, because God raised Him from the dead. Death could not hold Him because He was God. They knew from Psalms 110 verse 1 that God had called Him back to heaven, ready to yet return, and still able to give them the Kingdom. Peter confirmed His death, burial, and resurrection, but Les maintains Peter did not ascribe salvation to that death, burial, and resurrection; he stated it as a fact—they killed Him, but that did not stop God, because God raised Him and He is alive.