Slay them not, lest my people forget - The meaning of this seems to be, Do not destroy them at once, lest, being removed out of the way, the people should forget what was done, or should lose the impression which it is desirable should be produced by their punishment. Let them live, and let them wander about, as exiles under the divine displeasure, that they may be permanent and enduring proofs of the justice of God; of the evil of sin; of the danger of violating the divine law. So Cain wandered on the earth Genesis 4:12-14, a living proof of that justice which avenges murder; and so the Jews still wander, a lasting illustration of the justice which followed their rejection of the Messiah. The prayer of the psalmist, therefore, is that the fullest expression might be given to the divine sense of the wrong which his enemies had done, that the salutary lesson might not be soon forgotten, but might be permanent and enduring.
Scatter them by thy, power - Break up their combinations, and let them go abroad as separate wanderers, proclaiming everywhere, by being thus vagabonds on the earth, the justice of God.
And bring them down - Humble them. Show them their weakness. Show them that they have not power to contend against God.
O Lord our shield - See Psalms 5:12, note; Psalms 33:20, note. The words “our” here, and “my” in the former part of the verse, are designed to show that the author of the psalm regarded God as “his” God, and the people of the land as “his,” in the sense that he was identified with them, and felt that his cause was really that of the people.