128 “Your testimonies are wonderful: therefore has my soul searched them”. Who counts, even by their kinds, the testimonies of God? Heaven and earth, His visible and invisible works, declare in some manner the testimony of His goodness and greatness; and the very ordinary and accustomed course of nature, whereby the seasons are rapidly revolved, in all things after their kinds, however temporal and perishable, however held cheap through our constant experience of them, give, if a pious thinker give heed to them, a testimony to the Creator. But which of these is not wonderful, if we measure each not by its habitual presence, but by reason? But if we venture to bring all nature within the comprehensive view of one act of contemplation, does not that take place in us which the prophet describes, “I considered Your works, and trembled”? Yet the Psalmist was not terrified in his wonder at creation, but rather said that this was the reason that he ought to search it, because it was wonderful. For after saying, “Your testimonies are wonderful,” he adds, “therefore has my soul searched them;” as if he had become more curious from the difficulty of thoroughly searching them. For the more abstruse are the causes of anything, the more wonderful it is...
129. “When your word goes forth,” he says, “it gives light, and makes His little ones to understand”. What is the little one save the humble and weak? Be not proud therefore, presume not in your own strength, which is nought; and you will understand why a good law was given by a good God, though it cannot give life. For it was given for this end, that it might make you a little one instead of great, that it might show that you had not strength to do the law of your own power: and that thus, wanting aid and destitute, you might fly unto grace, saying, “Have mercy upon me, O Lord, for I am weak.”...Let all be little ones, and let all the world be guilty before You: because “by the deeds of the Law there shall no flesh be justified” in Your sight; “for by the Law is the knowledge of sin,” etc. These are Your wonderful testimonies, which the soul of this little one has searched; and has therefore found, because he became humbled and a little one. For who does Your commandments as they ought to be done, that is, by “faith which works through love,” save love itself be shed abroad in his heart through the Holy Spirit?
130. This is confessed by this little one; “I opened my mouth,” he says, “and drew in the spirit: for I longed for Your commandments”. What did he long for, save to obey the divine commandments? But there was no possibility of the weak doing hard things, the little one great things: he opened his mouth, confessing that he could not do them of himself: and drew in power to do them: he opened his mouth, by seeking, asking, knocking: and thirsty drank in the good Spirit, which enabled him to do what he could not do by himself, “the commandment holy and just and good.” Not that they themselves who “are led by the Spirit of God,” do nothing; but that they may not do nothing good, they are moved to act by the good Spirit. For so much the more is every man made a good son, in proportion as the good Spirit is given unto Him by the Father in a greater measure.
131. He still prays. He has opened his mouth, and drawn in the Spirit; but he still knocks in prayer unto the Father, and seeks: he drinks, but the more sweet he finds it, the more eagerly does he thirst. Hear the words of him in his thirst. “O look Thou upon me,” he says, “and be merciful unto me: according to the judgment of those that love Your Name”: that is, according to the judgment You have dealt unto all who love Your Name; since You have first loved them, to cause them to love You. For thus says the Apostle John, “We love God, because He first loved us.”
132. See what the Psalmist next most openly says: “Order my steps after Your word: and so shall no wickedness have dominion over me”. Where what else does he say than this, Make me upright and free according to Your promise. But so much the more as the love of God reigns in every man, so much the less has wickedness dominion over him. What else then does he seek than that by the gift of God he may love God? For by loving God he loves himself, so that he may healthily love his neighbour also as himself: on which commandments hang all the Law and the Prophets. What then does he pray, save that God may cause the fulfillment by His help of those commandments which He imposes by His bidding?
133. But what means this that he says, “O deliver me from the calumnies of men: so shall I keep Your commandments”?...Did not the holy people of God much the more gloriously keep the commandments among these very calumnies, when they were at their hottest in the midst of tribulations, when they yielded not to their persecutors to commit impieties? But, in truth, the meaning of these words is this: Do Thou, by pouring upon me Your Spirit, guard me from being overcome by the terrors of human calumny, and from being drawn over to their evil deeds away from Your commandments. For if You have thus dealt with me, that is, if You have in this manner delivered me by the gift of patience from their calumnies, so that I fear not the false charges they prefer against me; among those very calumnies I will keep Your commandments.
134. “Show the light of Your countenance on Your servant, and teach me your statutes”: that is, manifest Your presence, by succouring and aiding me. “And teach me Your righteousnesses.” Teach me to work them: as it is more plainly expressed elsewhere, “Teach me to do Your will.” For they who hear, although they retain in their memories what they hear, are by no means to be considered to have learned, unless they do. For it is the word of Truth: “Every man that has heard and has learned of the Father, comes unto Me.” He therefore who obeys not in deed, that is, who comes not, has not learned.
135. “My eyes have descended streams of waters, because they have not kept Your law”: that is, my eyes. For in some copies there is this reading, “Because I have not kept Your law, streams of waters” therefore “descended,” that is, floods of tears....
Source: The Enarrations, or Expositions, on the Psalms (New Advent)