John Calvin Commentary Psalms 101:1

"I will sing of lovingkindness and justice: Unto thee, O Jehovah, will I sing praises." — Psalms 101:1 (ASV)

I will sing of mercy and of judgment—what David here says about singing must be understood by the reader as indicating that this psalm contains the substance of his own meditations about what kind of king he would be, whenever he would be put in possession of the sovereign power that had been promised him.

To sing, therefore, of mercy and of judgment is equivalent to declaring in solemn terms that he would be a just and upright king. Augustine understands this as meaning that God is to be praised, whether He punishes people with severity or whether He shows Himself merciful to them; but this interpretation is too refined.

David does not speak of God’s secret judgments, but of the due administration of the kingdom, so that he might fulfill his vocation both by words and deeds. When he asserts, Unto thee, O Jehovah! will I sing psalms, he acknowledges that it was by the favor of God that he was appointed to so distinguished and honorable an office; for it would have been an act of presumptuous rashness for him to have thrust himself into it at the mere impulse of his own mind.

He very properly comprehends all princely virtues under these two particulars, mercy and judgment; for as it is the principal duty of a king to grant to every person their own right, so he is also required to possess a considerate love and compassion towards his subjects. Solomon therefore justly says, (Proverbs 16:12) The throne is established by righteousness.