Albert Barnes Commentary Psalms 110:7

"He will drink of the brook in the way: Therefore will he lift up the head." — Psalms 110:7 (ASV)

He shall drink of the brook in the way - The design here seems to be to represent the Messiah as a victorious king and conqueror pursuing his enemies. In the previous verse, the psalmist had represented him under the image of one engaged in battle, slaying his enemies with a great slaughter. Here, he represents him as pursuing those who escape from the battle, and as pursuing them without fainting or exhaustion. He is like one who finds abundant springs and streams of water in his travels; who refreshes himself at those fountains and streams; and who, therefore, is not faint or weary. He pursues his foes vigorously and with success.

Therefore shall he lift up the head - Therefore, he shall triumph, or be successful. The head falls when we are faint and exhausted, when we are disappointed and ashamed, or when we are conscious of guilt. It is lifted up in conscious rectitude, in success and triumph, and in the exuberance of hope.

The idea here is that the Messiah would be triumphant. He would achieve victory over all his foes; he would pursue his flying enemies without exhaustion and return from the conquest joyous, exulting, and triumphant. All this is under the image of a victorious hero. All this will be accomplished in the conquest of the world by the Gospel; in the subduing of the foes of God; in the final scene when the Redeemer shall deliver up the kingdom to God (1 Corinthians 15:24–28).