David
Psalm 4:3ESV·traditional attribution

But know that the LORD has set apart the godly for himself; the LORD hears when I call to him.

John Calvin Reformed @genevareformer

PSALM 4. After David in the beginning of the psalm has prayed to God to help him, he immediately turns his discourse to his enemies, and depending on the promise of God, triumphs over them as a conqueror. He, therefore, teaches us by his example, that as often as we are weighed down by adversity, or involved in very great distress, we ought to meditate...

Commenting on Psalm 4:1-8

C.H. Spurgeon Reformed Baptist @princeofpreachers

"But know." Fools will not learn, and therefore they must again and again be told the same thing, especially when it is such a bitter truth which is to be taught them, viz.:—the fact that the godly are the chosen of God, and are, by distinguishing grace, set apart and separated from among men.

Matthew Henry Presbyterian @wholebiblehenry

The title of the psalm acquaints us that David, having penned it by divine inspiration for the use of the church, delivered it to the chief musician, or master of the song, who (according to the divine appointment of psalmody made in his time, which he was chiefly instrumental in the establishment of) presided in that service.

Commenting on Psalm 4:1-5