The Pulpit Commentary
Judge me, O God (comp. Psa_35:24). And plead my cause. (comp. Psa_35:1). God's intervention is asked in the struggle between David and his enemies, on the assumed ground that he is in the right, and not they. God will, of course, only interpose if this is so. Against an ungodly nation; or, an unkind, unloving nation. Though called גוִי, as in Isa_1:4, still Israel is meant. They were "unloving," both towards God and towards their king. O deliver me from the deceitful and unjust man. Either Absalom or Ahithophel may be meant; or "man" may be used abstractedly for David's enemies generally.

The Pulpit Commentary
For thou art the God of my strength; i.e. the God in whom is all my strength (Psa_28:7). Why dost thou cast me off? An equivalent to the "Why hast thou forgotten me?" of Psa_42:9. Why go I mourning because of the oppression of the enemy? Repeated, with the variation of a single word, from Psa_42:9.

The Pulpit Commentary
O send out thy light and thy truth (Psa_40:11; Psa_57:3, where, however, "mercy (חסד) and truth" take the place of "light and truth"). Both words equally signify God's favour. Let them lead me. As the pillar of fire and of the cloud led the Israelites into the promised land, so let God's "light and truth" now lead David back to Jerusalem and God's "holy hill of Zion." Let them bring me unto thy holy hill, and to thy tabernacles; or, thy dwelling-place. In his exile it was David's most earnest desire to revisit the tabernacle which he had set up on Mount Zion, where God's presence dwelt, and prayer was most acceptably offered (see 2Sa_15:25; Psa_42:2). He had made his being brought back to it a test of the return of God's favour (2Sa_15:25, 2Sa_15:26).

The Pulpit Commentary
Then will I go unto the altar Of God. As the special place where thanksgiving ought to be made, and sacrifice offered (see 2Sa_6:17; 1Ch_16:1). Unto God my exceeding Joy; literally, unto God the gladness of my exultation. Yea, upon the harp will I praise thee, O God my God. The psalmist has before him some such scene as that depicted in 2Sa_6:1-23. and 1Ch_15:25-29, where, amid shouts and singing and dancing, and "with sound of the cornet, and with trumpets, and with cymbals, with psalteries and harps," a joyful procession approached the tabernacle, David himself taking part in it.

The Pulpit Commentary
Why art thou cast down, O my soul? and why art thou disquieted within me? hope in God: for I shall yet praise him, who is the health of my countenance, and my God. The refrain of Psa_42:11 is here repeated totidem verbis; and the plaint of the exiled monarch is brought to an end. The burden of the refrain is hope and confidence. Notwithstanding the woes of the present, the writer has no doubt in respect of the future; he will yet have occasion to "praise" God, whom he feels to be "his God—his Health and Salvation.