Adam Clarke on Psalms 101:1

I will sing of mercy and judgment - David might say, Adverse and prosperous providences have been of the utmost use to my soul; therefore, I will thank God for both. Or, as he was probably now called to the government of all the tribes, he might make a resolution that he would show חסד chesed, incessant benevolence, to the upright; and משפט mishpat, the execution of judgment, to the wicked; and would make the conduct of God the model of his own.