John Calvin Commentary Psalms 119:122

"Be surety for thy servant for good: Let not the proud oppress me." — Psalms 119:122 (ASV)

Become surety for your servant for good. This prayer is almost similar to that of the preceding verse, for I prefer translating the Hebrew verb ערוב, arob, by Become surety for, to rendering, as others do, Delight your servant in good, or Make your servant to delight in good. According to this second version, the words are a prayer that God would rejoice his servant with his benefits.

There is a third translation, by which they become a prayer that God would inspire his heart with the love and desire of rectitude, for true perfection consists in our taking pleasure in justice and uprightness. But as from the last clause of the verse it is obvious that David here desires help against his enemies, the verb Become surety is the more appropriate rendering. It is as if he had said: "Lord, since the proud cruelly rush upon me to destroy me, interpose yourself between us, as if you were my surety."

The letter ל, lamed, which signifies for, is not prefixed to the noun, but this is no valid objection to our translation, as that letter is often understood. It is a form of expression full of comfort to represent God as performing the office of a surety to effect our deliverance. He is said metaphorically to become surety for us, just as if, on finding us indebted in a large sum of money, he discharged us from the obligation by paying down the money to our creditor.

The prayer is to this effect: that God would not allow the wicked to exercise their cruelty against us at their pleasure, but that he would interpose as a defender to save us. By these words, the Prophet intimates that he was in extreme danger and had nothing else left him in which to hope but the help of God.