15 But it might occur to one; if because of sins man was held by the devil, have sins pleased Christ, who saved the needy man from the mighty? Far be it. But “He it is that shall spare the helpless and poor man”: that is, shall remit sins to the man, humble and not trusting in his own merits, or hoping for salvation because of his own virtue, but needing the grace of his Saviour. But when he has added, “and the souls of the poor He shall save:” he has recommended to our notice both the aids of grace; both that which is for the remission of sins, when he says, “He shall spare the poor and needy man;” and that which does consist in the imparting of righteousness, when he has added, “and the souls of the poor He shall save.” For no one is meet of himself for salvation (which salvation is perfect righteousness), unless God's grace aid: because the fullness of the law is nought but love, which does not exist in us of ourselves, but is shed abroad in our hearts through the Holy Spirit which has been given unto us.
16. “From usuries and iniquity He shall redeem the souls of them”. What are these usuries but sins, which are also called debts? But I think they have been called usuries, because more of ill is found in the punishments than has been committed in the sins. For, for example's sake, while a man-slayer kills only the body of a man, but can no wise hurt the soul; of himself both soul and body is destroyed in hell. Because of such despisers of present commandment and deriders of future punishment has been said, “I coming would have exacted with usuries,” from these usuries are redeemed the souls of the poor by that blood which has been shed for the remission of sins. He shall redeem, I say, from usuries, by remitting sins which owed larger punishments: but He shall redeem from iniquity, by helping them by grace even to do righteousness. Therefore the same two things have been repeated which were said above. For in that which is above, “He shall spare the helpless and poor man,” there is understood “from usuries:” but in that which there he says, “and the souls of the poor He shall save;” there seems to have been implied, “from iniquity:” so that the words “He shall redeem,” are understood with both. So when He shall spare the poor and helpless man, and shall save the souls of the poor: thus “from usuries and iniquity He shall redeem the souls of them. And honourable shall be the name of Him in the presence of them.” For they give honour to His name for so great benefits, and they respond that “meet and right it is” to render thanks to the Lord their God. Or, as some copies have it, “and honourable is the name of them in the presence of Him:” for even if Christians seem despicable to this world, the name of them in the presence of Him is honourable, who to them has given it, no longer remembering those names in His lips, whereby before they used to be called, when they were bound fast by the superstitions of the Gentiles, or signed with names derived from their own evil deserts, before they were Christians, which name is honourable in the presence of Him, even if it seems despicable to enemies.
17. “And He shall live, and there shall be given to Him of the gold of Arabia”. There would not have been said, “and He shall live” (for of whom could not this be said, though living for ever so brief a space of time on this earth?) unless that life were being recommended to our notice, wherein He “dies no more, and death over Him shall have no more dominion.” And thus, “and He shall live,” that was despised in death: for, as another Prophet says, “there shall be taken away from the earth the life of Him.” But what is, “and there shall be given to Him of the gold of Arabia”? For the fact that from thence even the former Salomon received gold, in this Psalm has been in a figure transferred unto another true Salomon, that is, the true Peace-maker. For the former did not have dominion “from the river even unto the ends of the round world.” Thus then has been prophesied, that even the wise men of this world in Christ would believe. But by Arabia we understand the Gentiles; by gold wisdom which does as much excel among all doctrines as gold among metals. Whence has been written, “Receive ye prudence as silver, and wisdom as proved gold.” “And they shall pray concerning Himself always.” That which the Greek has, περὶ αὐτοῦ, some have interpreted by “concerning Himself,” some “for Himself,” or “for Him.” But what is, “concerning Himself,” except perchance that for which we pray, saying, “Your kingdom come”? For Christ's coming shall make present to believers the kingdom of God. But how to understand “for Him” is difficult; except that when prayer is made for the Church, for Himself prayer is made, because she is His Body. For concerning Christ and the Church has been sent before a great Sacrament, “there shall be two in one flesh.” But now that which follows, “all the day long,” that is, in all time, “they shall bless Him,” is sufficiently evident.
Source: The Enarrations, or Expositions, on the Psalms (New Advent)