NOTES for Psa 149:1-9
The question comes up very often: should one read psalms that curse enemies, now that there is already a New Testament, which has set entirely different tasks before us? After all, even in the psalm most filled with praise and glorification of God, one can find curses and thirst for every possible punishment upon enemies. It appears that nothing contradicts the spirit of the Gospel so sharply.
This apparent contradiction is resolved rather simply: these enemies are not our enemies, but the enemies of God and of Christ, who forgave His executioners and Peter, but sternly denounced the Pharisees and the "world." These enemies of God are not only outside, somewhere far away, but also within us ourselves: they are our sins. Then reading the psalms can protect us from lukewarmness by stirring up our hatred not against sinners, but against evil and sin.