Slay them not, lest my people forget: scatter them by thy power; and bring them down, O Lord our shield.
Slay them not, lest my people forget - Slay not the race, while thou consumest (Psalms 59:13) the individuals hostile to the Lord's anointed. Let the race survive as a lasting monument of God's righteous judgments on transgressors (1 Samuel 2:36; 2 Samuel 3:29). Such has been the doom of the Jewish nation for their rejection of Messiah. While hundreds of thousands have been destroyed, the race has been kept from extinction as a monument of the wrath of God. "My people" are the professing people of God, who are warned by the fate of Israel (Romans 11:20-21) of the fatal effects of unbelief.
Scatter them by thy power. The Jews, scattered in all lands, are the living witnesses to God's power and punitive justice, like their prototype Cain, 'fugitives and vagabonds in the earth,' bearing the brand of the murder of the Holy One wheresoever they go (Genesis 4:12-15), Compare Psalms 109:10-15. "Thy power" stands in contrast to the power of the godless enemies who thought themselves invincible. "Scatter them " stands in contrast to their having "gathered" themselves together against the Psalmist (Psalms 59:3).
Bring them down - from their high place of pride, arising out of prosperity.
O Lord our shield. Our implies that David's cause is that of the whole Church. Hence, in Psalms 59:5 he calls upon the God of Israel. The cause of righteousness was at stake in his person, and would have suffered injury if Saul had prevailed.