Charles H. Spurgeon on Psalms 119:122

Be surety for thy servant for good. There are three expositions of this clause, as noting the end, the cause, the event.

1. Undertake for me, ut sire bonus et justus, so Rabbi Arama on the place; surety for me that I may be good. Theodoret expounds it, "Undertake that I shall make good my resolution of keeping thy law." He that joins, undertakes; though we have precepts and without God's undertaking we shall never be able to perform our duty.

2. Undertake for me to help me in doing good; so some read it: would not take his part in an evil cause. To commend a wrong to God's protection, is to provoke him to hasten our punishment, to us serve under our oppressors; but, when we have a good cause, and good conscience, he will own us. We cannot expect he should maintain us and bear us out in the Devil's service, wherein we have entangled selves by our own sin.

3. Be with me for good: so it is often rendered: "Shew me a token for good" (Psalms 86:17); "Pray not for this people for good" (Jeremiah 11:14); so, "Remember me, O my God, for good" (Nehemiah 13:31). So here "Be surety for thy servant for good." Thomas Manton.