The Psalmist proceeds a step farther in the 4th verse, declaring that God stretched forth his hand to give him succor, because he was unrighteously afflicted by his enemies. And surely if we desire to be favored with the assistance of God, we ought to see to it that we fight under his standard. David, therefore, calls him a judge of righteousness, or, which is the same thing, a righteous judge; as if he had said, God has acted towards me according to his ordinary manner and constant principle of acting, for it is his usual way to undertake the defense of good causes. I am more inclined to render the words, Thou sittest a just judge, than to render them, O just judge, thou sittest, because the form of expression, according to the first reading, is more emphatic. The import of it is this: God at length has assumed the character of judge, and is gone up into his judgment-seat to execute the office of judge. On this account he glories in having law and right on his side, and declares that God was the maintainer of his right and cause. What follows in the next verse, Thou hast destroyed [or discomfited,] the wicked, belongs also to the same subject. When he beholds his enemies overthrown, he does not rejoice in their destruction, considered simply in itself; but in condemning them on account of their unrighteousness, he says that they have received the punishment which they deserved. Under the name of nations he means, that it was not a small number of ungodly persons who were destroyed, but great armies, yea, even all who had risen up against him from different quarters. And the goodness of God shines forth the brighter in this, that, on account of the favor which he bare to one of his servants, he spared not even whole nations. When he says, Thou hast blotted out their name for ever, it may be understood as meaning, that they were destroyed without any hope of ever being able to rise again, and devoted to everlasting shame. We could not otherwise discern how God buries the name of the ungodly with themselves, did we not hear him declare that the memory of the righteous shall be for ever blessed, (Proverbs 10:7.)

For thou hast maintained my right and my cause - My righteous cause; that is, when he was unequally attacked. When his enemies came upon him in an unprovoked and cruel manner, God had interposed and had defended his cause. This shows that the psalmist refers to something that had occurred in the past; also that he regarded his cause as right - for the interposition of God in his behalf had confirmed him in this belief.
Thou satest in the throne judging right - As if he had been seated on a bench of justice, and bad decided on the merits of his cause before he interfered in his behalf. It was not the result of impulse, folly, partiality, or favoritism; it was because he had, as a judge, considered the matter, and had decided that the right was with the author of the psalm, and not with his enemies. As the result of that determination of the case, he had interposed to vindicate him, and to overthrow his adversaries. Compare Psalm 8:3-8.

For (b) thou hast maintained my right and my cause; thou satest in the throne judging right.
(b) However the enemy seems for a time to prevail yet God preserves the just.

For thou hast maintained my right and my cause,.... Or vindicated and established his righteous cause; God had pleaded and defended it, and by the flight, fall, and ruin of his enemies, had clearly made it appear that his cause was just and good;
thou sittest in the throne judging right; God has not only a throne of grace on which he sits, and from whence he distributes grace and mercy to his people, but he has a throne of judgment, and which is prepared for it, as in Psalm 9:7; where he sits as the Judge of all the earth, and will do right; nor can he do otherwise, though his judgments are not always manifest in the present state of things; and the vindication of the psalmist's innocence and uprightness is another reason of his joy and gladness.