27 Let not therefore heretics flatter themselves against me, because I said, “the shortness of my days,” as if they would not last down to the end of the world. For what has he added? “O my God, take me not away in the midst of my days”. Deal Thou not with me according as heretics speak. Lead me on unto the end of the world, not only to the middle of my days; and finish my short days, that You may afterwards grant unto me eternal days. Wherefore then have you asked concerning the shortness of your days? Wherefore? Do you wish to hear? “Your years are in the generation of generations.” This is why I asked concerning those short days, because although my days should endure unto the end of the world, yet they are short in comparison of Your days. For “Your years are in the generation of generations.” Wherefore does he not say, Your years are unto worlds of worlds; for thus rather is eternity usually signified in the holy Scriptures; but he says, “Your years are in the generation of generations”? But what are your years? What, but those which do not come, and then pass away? What, but they which come not, so as to cease again? For every day in this season so comes as to cease again; every hour, every month, every year; nothing of these is stationary; before it has come, it is to be; after it has come, it will not be. Those everlasting years of yours, therefore, those years that are not changed, “are in the generation of generations.” There is a “generation of generations;” in that shall your years be. There is one such, and if we acknowledge it aright, we shall be in it, and the years of God shall be in us. How shall they be in us? Just as God Himself shall be in us: whence it is said, “That God may be all in all.” For the years of God, and God Himself, are not different: but the years of God are the eternity of God: eternity is the very substance of God, which has nothing changeable; there nothing is past, as if it were no longer: nothing is future, as if it existed not as yet. There is nothing there but, Is: there is not there, Was, and Will be; because what was, is now no longer: and what will be, is not as yet: but whatever is there, simply Is....Behold this great I Am! What is man's being to this? To this great I Am, what is man, whatever he be? Who can understand that To Be? Who can share it? Who can pant, aspire, presume that he may be there? Despair not, human frailty! “I am,” He says, “the God of Abraham, and the God of Isaac, and the God of Jacob.” You have heard what I am in Myself: now hear what I am on your account. This eternity then has called us, and the Word burst forth from eternity. It is now eternity, it is now the Word, and no longer time.
28....From so many generations you will gather together all the holy offspring of all generations, and wilt form one generation thence: “In” this “generation of generations are Your years,” that is, that eternity will be in that generation, which is collected from all generations, and reduced into one; this shall share in Your eternity. Other generations are born for fulfilling their times, out of which this one is regenerated for ever; though changed it shall be endued with life, it shall be fitted to bear You, receiving strength from You.
29. “You, Lord, in the beginning hast laid the foundation of the earth: and the Heavens are the work of Your hands”....God laid the foundation of the earth, we know: the heavens are the works of His hands. For do not imagine that God does one thing with His hand, another by His word. What He does by His word, He does by His hand: for He has not distinct bodily members, who said, “I Am That I Am.” And perhaps His Word is His hand, assuredly His hand is His power. For inasmuch as it is said, “Let there be a firmament,” and there was a firmament; He is understood to have created it by His Word; but when He said, “Let Us make man in Our image, after Our likeness;” He seems to have created him by His hand. Hear therefore: “The heavens are the work of Your hands.” Lo, what He created by His word, He created also by His hands; because He created them through His excellence, through His power. Observe rather what He created, and seek not to know in what manner He created them. It is much to you to understand how He created them, since He created yourself so, that you may first be a servant obeying, and afterwards perhaps a friend understanding.
30. “They shall perish, but You shall endure”. The Apostle Peter says this openly: “By the word of God the heavens were of old,” etc. He has said then that the heavens have already perished by the flood: and we know that the heavens perished as far as the extent of this atmosphere of ours. For the water increased, and filled the whole of that space in which birds fly; thus perished the heavens that are near the earth; those heavens which are meant when we speak of the birds of heaven. But there are heavens of heavens higher than these in the firmament: but whether these also shall perish by fire, or those only which perished also by the flood, is a much harder question among the learned, nor can it easily, especially in a limited space of time, be explained. Let us therefore dismiss or put it off; nevertheless, let us know that these things perish, and that God endures....
Source: The Enarrations, or Expositions, on the Psalms (New Advent)