166 Let us now hear the words of one praying: since we know who is praying, and we recognise ourselves, if we be not reprobate, among the members of this one praying. “Let my prayer come near in Your sight, O Lord”: for, “The Lord is near unto them that are of a contrite heart.” “Give me understanding, according to Your word.” He claims a promise. For he says, “according to Your word,” which is to say, according to Your promise. For the Lord promised this when He said, “I will inform you.”
167. “Let my request come before Your presence, O Lord: deliver me, according to Your word”. He repeats what he has asked. For his former words, “Let my prayer come near in Your presence, O Lord:” are like what he says, “Let my request come before Your presence, O Lord:” and the words, “Give me understanding according to Your word,” agree with these, “Deliver me according to Your word.” For by receiving understanding he is delivered, who of himself through want of understanding is deceived.
168. “My lips shall burst forth praise: when You have taught me Your righteousnesses”. We know how God teaches those who are docile unto God. For every one who has heard from the Father and has learned, comes unto Him “who justifies the ungodly:” so that he may keep the righteousnesses of God not only by retaining them in his memory, but also by doing them. Thus does he who glories, glory not in himself, but in the Lord, and burst forth praise.
169. But as he has now learned, and praised God his Teacher, he next wishes to teach. “Yea, my tongue shall declare Your word: for all Your commandments are righteousness”. When he says that he will declare these things, he becomes a minister of the word. For though God teach within, nevertheless “faith comes from hearing: and how do they hear without a preacher?” For, because “God gives the increase,” is no reason why we need not plant and water.
170. “Let Your hand be stretched forth (fiat, be made) to save me, for I have chosen Your commandments”. That I might not fear, and that not only might my heart hold fast, but my tongue also utter Your words: “I have chosen Your commandments,” and have stifled fear with love. Let Your hand therefore be stretched forth, to save me from another's hand. Thus God saved the Martyrs, when He permitted them not to be slain in their souls: for “vain is the safety of man” in the flesh. The words, “Let Your hand be made,” may also be taken to mean Christ the Hand of God...Certainly where we read the following words, “I have longed for Your salvation, O Lord”: even if all our foes be reluctant, let Christ the Salvation of God occur to us: the righteous men of old confess that they longed for Him, the Church longed for His destined coming from His mother's womb, the Church longs for His coming at His Father's right hand. Subjoined to this sentence are the words, “And Your law is my meditation:” for the Law gives testimony unto Christ.
171. But in this faith, though the heathen rage furiously, and the people imagine a vain thing: though the flesh be slain while it preaches You: “My soul shall live, and shall praise You: and Your judgments shall help me”. These are those judgments, which it was time should begin at the house of the Lord. But “they will help me,” he says. And who cannot see how much the blood of the Church has aided the Church? How great a harvest has risen in the whole world from that sowing?
172. At last he opens himself completely, and shows what person was speaking throughout the whole Psalm. “I have gone astray,” he says, “like a sheep that is lost: O seek Your servant, for I do not forget Your commandments”. Let the lost sheep be sought, let the lost sheep be quickened, for whose sake its Shepherd left the ninety and nine in the wilderness, and while seeking it, was torn by Jewish thorns. But it is still being sought, let it still be sought, partly found let it still be sought. For as to that company, among whom the Psalmist says, “I do not forget Your commandments,” it has been found; but through those who choose the commandments of God, gather them together, love them, it is still sought, and by means of the blood of its Shepherd shed and sprinkled abroad, it is found in all nations.
Source: The Enarrations, or Expositions, on the Psalms (New Advent)