I have known; that God, etc. There can be no question that David here seals or corroborates his prayer by turning his thoughts and discourse to the providential judgments of God, for, as I have already said, doubtful prayer is no prayer at all. He declares it to be a thing known and ascertained that God cannot but deliver the afflicted. As he may connive for a time, however, and suffer good and upright persons to be grievously tried, David suggests as consideration which may meet this temptation, that God does so advisedly, that he may relieve those who are in affliction, and recover those who are oppressed. He accordingly says in express words that he will be the judge of the poor and the afflicted. In this way does he encourage both others and himself under continued troubles, till the time proper for deliverance arrive, intimating that though he might be universally considered an object of pity in being exposed to the fury of the wicked, and in not being immediately delivered by the hand of God, he would not give way to despair, but remember that it was the very part of God to undertake the cause of the poor. It were to weaken the passage if we considered David merely to be speaking of his own individual case. He infers (Psalm 140:13) that the righteous would give thanks to God, and be safe under his help. For the particle 'k, ach, which is often adversative in the Hebrew, is here affirmative, and denotes inference or consequence from what was formerly stated. Though the godly may be silenced for a time, and through the force of trouble may not raise the praises of God, David expresses his conviction that what was taken away would be speedily restored, and they would celebrate the loving kindness of the Lord with joy and alacrity. As this is not easily believed in circumstances of trial, the already referred to is inserted. We must endeavor, though with a struggle, to rise to a confident persuasion, that however low they may be brought, the Lord's people will be restored to prosperity, and will soon sing his praises. The second clause of the verse gives the reason of their thanksgiving's. He speaks of this as being the ground of the praises of the righteous, that they experience God's care of them, and concern for their salvation. For to dwell before God's face is to be cherished and sustained by his fatherly regards.

I know that the Lord will maintain the cause of the afflicted - See the notes at Psalm 9:4. The psalmist here doubtless refers primarily to himself, as having a confident belief that the Lord would maintain "his" cause, or would defend "him." At the same time he makes the statement general, implying that what would be done to him would be done to all in similar circumstances. The idea is that God, in all his attributes, in all his providential arrangements, in all his interpositions on earth, would be found to be on the side of the oppressed, the afflicted, and the wronged. He has no attribute that can take part with an oppressor or a wrong doer. The wicked cannot come to him with the belief that he will be on their side: the righteous - the oppressed - the afflicted - can.
And the right of the poor - He will defend the right of the poor. Literally, "The judgment of the poor." That which will be just and right in their case.

The cause of the afflicted - Every person who is persecuted for righteousness' sake has God for his peculiar help and refuge; and the persecutor has the same God for his especial enemy.

I know,.... Here is a double reading: the "Keri", or marginal reading, is, "thou knowest"; an appeal of the psalmist to God, who knew the thoughts of the wicked concerning him, and their devices against him; as Kimchi: but the Scripture reading is, I know; expressing his full persuasion and assurance
that the Lord will maintain the cause of the afflicted, and the right of the poor; of his poor and afflicted people, that are afflicted within and without, by men and devils; and who are poor as to the things of this world, and poor in spirit, and sensible of their spiritual poverty, but rich in grace: the cause of these God will maintain against their oppressors, and right their wrongs, and avenge their injuries; this the psalmist knew, and was assured of from the word of God, from instances and examples in former times, and from his own experience, Psalm 9:4.

(Compare Psalm 9:4).

With Psalm 140:13 the mood and language now again become cheerful, the rage has spent itself; therefore the style and tone are now changed, and the Psalm trips along merrily as it were to the close. With reference to ידעת for ידעתי (as in Job 42:2), vid., Psalm 16:2. That which David in Psalm 9:5 confidently expects on his own behalf is here generalized into the certain prospect of the triumph of the good cause in the person of all its representatives at that time oppressed. אך, like ידעתּי, is an expression of certainty. After seeming abandonment God again makes Himself known to His own, and those whom they wanted to sweep away out of the land of the living have an ever sure dwelling-place with His joyful countenance (Psalm 16:11).