5 Let us see then what God has sworn. “I have sworn,” He says, “to David My servant; your seed will I establish for ever”. But what is the seed of David, but that of Abraham. And what is the seed of Abraham? “And to your seed,” He says, “which is Christ.” But perhaps that Christ, the Head of the Church, the Saviour of the body, is the seed of Abraham, and therefore of David; but we are not Abraham's seed? We are assuredly; as the Apostle says, “And if you be Christ's, then are you Abraham's seed, and heirs according to the promise.” In this sense, then, let us take the words, brethren, “Your seed will I establish for ever,” not only of that Flesh of Christ, born of the Virgin Mary, but also of all of us who believe in Christ, for we are limbs of that Head. This body cannot be deprived of its Head: if the Head is in glory for ever, so are the limbs, so that Christ remains entire for ever. “Your seed will I establish for ever: and set up your throne to generation and generation.” We suppose he says, “for ever,” because it is “to generation and generation:” since he has said above, with “my mouth will I ever be showing Your truth to generation and generation.” What is “to generation and generation”? To every generation: for the word needed not as many repetitions, as the coming and passing away of the several generations. The multiplication of generations is signified and set forth to notice by the repetition. Are possibly two generations to be understood, as you are aware, my beloved brethren, and as I have before explained? For there is now a generation of flesh and blood: there will be a future generation in the resurrection of the dead. Christ is proclaimed here: He will be proclaimed there: here He is proclaimed, that He may be believed in: there, He will be welcomed, that He may be seen. “I will set up Your throne from one generation to another.” Christ has now a throne in us, His throne is set up in us: for unless he sat enthroned within us, He would not rule us: but if we were not ruled by Him, we should be thrown down by ourselves. He therefore sits within us, reigning over us: He sits also in another generation, which will come from the resurrection of the dead. Christ will reign for ever over His Saints. God has promised this; He has said it: if this is not enough, God has sworn it. As then the promise is certain, not on account of our deservings, but of His pity, no one ought to be afraid in proclaiming that which he cannot doubt of. Let that strength then inspire our hearts, whence Æthan received his name, “strong in heart:” let us preach the truth of God, the utterance of God, His promises, His oath; and let us, strengthened on every side by these means, glorify God, and by bearing Him along with us, become Heavens.
6. “O Lord, the very Heavens shall praise Your wondrous works”. The Heavens will not praise their own merits, but Your wondrous works, O Lord. For in every act of mercy on the lost, of justification of the unrighteous, what do we praise but the wondrous works of God? Thou praisest Him, because the dead have risen: praise Him yet more, because the lost are redeemed. What grace, what mercy of God! You see a man yesterday a whirlpool of drunkenness, today an ornament of sobriety: a man yesterday the sink of luxury, today the beauty of temperance: yesterday a blasphemer of God, today His praiser: yesterday the slave of the creature, today the worshipper of the Creator. From all these desperate states men are thus converted: let them not look at their own merits: let them become Heavens, and praise the wondrous works of Him by whom they were made Heavens....
7. “For who is he among the clouds, who shall be compared unto You, Lord!”. Is this to be the praise of the Heavens, is this to be their rain? What? Are the preachers confident, because “none among the clouds shall be compared unto the Lord”? Does it appear to you, brethren, a high ground of praise, that the clouds cannot be compared with their Creator? If it is taken in its literal, not in its mystical meaning, it is not so: what? Are the stars that are above the clouds to be compared with the Lord? What? Can the Sun, Moon, Angels, Heavens, be even compared with the Lord? Why is it then that he says, as if he meant some high praise, “For who is he among the clouds?” etc. We understand, my brethren, those clouds, as the Heavens, to be the preachers of truth; Prophets, Apostles, the announcers of the word of God....If therefore the clouds are the preachers of the truth, let us first enquire why they are clouds. For the same men are Heavens and clouds: Heavens from the brightness of the truth, clouds from the hidden things of the flesh: for all clouds are obscure, owing to their mortality: and they come and go. It is on account of these very obscurities of the flesh, that is, of the clouds, that the Apostle says, “Therefore judge nothing before the time, until the Lord come, who will bring to light the hidden things of darkness.” You see at this moment what a man is saying: but what he has in his heart, you cannot see: what is forced from the cloud, you see, what is kept within the cloud, you see not. For whose eyes pierce the cloud? The clouds therefore are the preachers of the truth in the flesh. The Creator of all things Himself came in the flesh....We are called clouds on account of the flesh, and we are preachers of the truth on account of the showers of the clouds: but our flesh comes in one way, His by another. We too are called sons of God, but He is the Son of God in another sense. His cloud comes from a Virgin, He is the Son from eternity, co-eternal with the Father. “Who is he then among the clouds, that shall be compared unto the Lord? And what is he among the sons of God, that shall be like the Lord?” Let the Lord Himself say whether He can find one like Himself. “Whom do men say that I the Son of Man am?” Because I appear, because I am seen, because I walk among you, and perhaps at present I have become common; say, whom do men say that I the Son of Man am? Surely when they see a son of man, they see a cloud; but say, “Whom do men say that I am?” In answer they gave Him the reports of men; “Some say that You are John the Baptist: some Elias, and others Jeremias, or one of the prophets.” Many clouds and sons of God are here mentioned: for because they were righteous and holy, as the sons of God, Jeremias, Elias, and John are called also sons of God: in their character of preachers of God, they are styled clouds. You have said what clouds men imagine Me to be: do ye too say, “Whom say ye that I am?” Peter replying in behalf of all, one for those who were one, answered, “You are the Christ, the Son of the living God;” not like those sons of God who are not made equal to You: You have come in the flesh: but not as the clouds, who are not to be compared unto You.
Source: The Enarrations, or Expositions, on the Psalms (New Advent)