8 “The law of the Lord is undefiled, converting souls”. The law of the Lord, therefore, is Himself who came to fulfil the law, not to destroy it; an undefiled law, “Who did no sin, neither was guile found in His mouth,” not oppressing souls with the yoke of bondage, but converting them to imitate Him in liberty. “The testimony of the Lord is sure, giving wisdom to babes.” “The testimony of the Lord is sure;” for, “no man knows the Father save the Son, and he to whomsoever the Son will reveal Him,” which things have been hidden from the wise and revealed to babes; for, “God resists the proud, but gives grace to the humble.”
Source: The Enarrations, or Expositions, on the Psalms (New Advent)