John Calvin Commentary Psalms 119:124

"Deal with thy servant according unto thy lovingkindness, And teach me thy statutes." — Psalms 119:124 (ASV)

Deal with your servant according to your goodness. The two clauses of this verse must be read correctly, for he does not first separately desire God to deal well with him, and next desire Him to be his master and teacher. He rather beseeches Him, in the exercise of that goodness and mercy which He is accustomed to display towards all His people, to instruct him in His law.

The object of the Prophet’s request then is that God would teach him His statutes. But he begins with the divine mercy, employing it as an argument to prevail with God to grant him what he desires. This prayer then must be understood as follows: Lord, deal gently with me, and manifest Your goodness towards me by instructing me in Your commandments.

Our whole happiness undoubtedly consists in our having that true wisdom which is to be derived from the word of God; and our only hope of obtaining this wisdom lies in God’s being pleased to display His mercy and goodness towards us. The Prophet, therefore, magnifies the greatness and excellence of the benefit of being instructed in the divine law when he requests that it may be bestowed upon him as a free gift.