8 “He shall abide for everlasting in the sight of God”; according to what, or because of what? “His mercy and truth who shall seek for Him?” He says also in another place, “All the ways of the Lord are mercy and truth, to men seeking His testament and His testimonies.” Large is the discourse of truth and mercy, but shortness we have promised. Briefly hear ye what is truth and mercy: because no small thing is that which has been said, “All the ways of the Lord are mercy and truth.” Mercy is spoken of, because our merits God regarded not, but His own goodness, in order that He might forgive us all our sins, and might promise life everlasting: but truth is spoken of, because He fails not to render those things which He has promised. Let us acknowledge it here, and let us do it; so that, just as to us God has shown forth His mercy and His truth, mercy in forgiving our sins, truth in showing forth His promises; so also, I say, let us execute mercy and truth, mercy concerning the weak, concerning the needy, concerning even our enemies; truth in not sinning, and in not adding sin upon sin....Who is therefore he that does this, save one out of those few, of whom is said, “He that shall have continued unto the end, the same shall be saved”? With reason here also “His mercy and truth who shall seek for Him?” Why is there “for Him”? “Who shall seek,” would be sufficient. Why has he added, “for Him,” but because many men seek to learn His mercy and truth in His books? And when they have learned, for themselves they live, not for Him; their own things they seek, not the things which are of Jesus Christ: they preach mercy and truth, and do not mercy and truth. But by preaching it, they know it: for they would not preach it, unless they knew it. But he that loves God and Christ, in preaching the mercy and truth of the Same, does himself seek her for Him, not for himself: that is, not in order that himself may have by this preaching temporal advantages, but in order that he may do good to His members, that is, His faithful ones, by ministering with truth of that which he knows: in order that he that lives, no longer for himself may live, but for Him that for all men has died.
9. “So I will play music to Your name, that I may render my vows from day unto day”. If you play music to the name of God, play not for a time. Will you for ever play? Will you for everlasting play? Render to Him your vows from day unto day. What is, render to Him your vows from day unto day? From this day unto that day. Continue to render vows in this day, until you come to that day: that is, “He that shall have continued even unto the end, the same shall be saved.”
Source: The Enarrations, or Expositions, on the Psalms (New Advent)