Albert Barnes Commentary Psalms 42:9

"I will say unto God my rock, Why hast thou forgotten me? Why go I mourning because of the oppression of the enemy?" — Psalms 42:9 (ASV)

I will say unto God my rock—I will appeal to God as my defense, my helper, my Savior. On the word "rock," as applied to God, see the notes at Psalm 18:2.

Why hast thou forgotten me?—See the notes at Psalm 22:1. He had seemed to forget and forsake him, for He did not come to interpose and save him. This is a part of the prayer that he says (Psalms 42:8) he would use.

Why go I mourning?—On the meaning of the word used here—קדר qodēr—see Psalm 35:14, note; Psalms 38:6, note. The idea is that of being bowed down, made sad, deeply afflicted, as one forsaken.

Because of the oppression of the enemy—In the oppression of the enemy; that is, during its continuance, or on account of it. The word here rendered “oppression” means distress, affliction, straits (Job 36:15; 1 Kings 22:27; Isaiah 30:20). The “enemy” here referred to may have been Absalom, who had driven him from his throne and kingdom.