Blessed is the man whom thou chastenest - תיסרנו teyasserennu, whom thou instructest; and teachest him out of thy law. Two points here are worthy of our most serious regard:
This is God's system of teaching; and the human intellect is his gift, which enables man to understand this teaching. We perhaps may add a third thing here; that as by sin the understanding is darkened, he gives the Holy Spirit to dispel this darkness from the intellect, in order that his word may be properly apprehended and understood. But he gives no new faculty; he removes the impediments from the old, and invigorates it by his Divine energy.
Blessed is the man whom thou chastenest, O Lord - “Happy the man;” or “Oh the blessedness of the man.” See the notes at Psalm 1:1. The word here rendered “chastenest” does not mean to chasten in the sense of afflicting or punishing. It means here to instruct; to warn; to admonish; to exhort. So the word is employed in Proverbs 9:7; Job 4:3; Psalm 16:7. The meaning here is, that the man is blessed or happy whom God so “instructs, warns, or teaches,” that he understands the principles of the divine administration. Such a man will see reasons for confidence in him in trouble, and for calmness of mind until punishment is brought upon his enemies.
And teachest him out of thy law - Causest him, from thy word, to understand the great principles of thy government.