Adam Clarke on 1 Corinthians 15:25

For he must reign, etc. - This is according to the promise, Psa 110:1 : "The Lord said unto my Lord, Sit thou at my right hand, until I make thine enemies thy footstool." Therefore the kingdom cannot be given up till all rule and government be cast down. So that while the world lasts, Jesus, as the Messiah and Mediator, must reign; and all human beings are properly his subjects, are under his government, and are accountable to him.