Charles H. Spurgeon on Psalms 119:137

Righteous art thou, O LORD, etc. Here David, sore troubled with grief for the wickedness of his enemies, yea, tempted greatly to impatience and distrust, by looking to their prosperous estate, notwithstanding their so gross impiety, doth now show unto us a three fold ground of comfort, which in this dangerous temptation upheld him. The first is, a consideration of that which God is in himself; namely, just and righteous: the second, a consideration of the equity of his word; the third, a view of his constant truth, declared in his working and doing according to his word. When we find ourselves tempted to distrust by looking to the prosperity of the wicked, let us look up to God, and consider his nature, his word, his works, and we shall find comfort.

Righteous art thou. This is the first ground of comfort a meditation of the righteousness of God's nature; he alters not with times, he changes not with persons, he is, alway and unto all, one and the same righteous and holy God. Righteousness is essential to him, it is himself; and he can no more defraud the godly of their promised comforts, not let the wicked go unpunished in their sins, than he can deny himself to be God, which is impossible. William Cowper.