For he must reign, etc. - This is according to the promise, Psalm 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.
For he must reign - It is fit, or proper ( δει dei), that he should reign until this is accomplished. It is proper that the mediatorial kingdom should continue till this great work is effected. The word “must” here refers to the propriety of this continuance of his reign, and to the fact that this was contemplated and predicted as the work which he would accomplish. He came to subdue all his enemies; see Psalm 2:6-10; or Psalm 110:1, “The Lord said unto my Lord, Sit thou at my right hand until I make thine enemies thy footstool.” Paul, doubtless, had this passage in his eye as affirming the necessity that he should reign until all his foes should be subdued. That this refers to the Messiah is abundantly clear from Matthew 22:44-45.