20 What next after youth? For, “You have taught me,” he says, “from my youth:” what after youth? For in that same first conversion of yours you learned, how before conversion you were not just, but iniquity preceded, in order that iniquity being banished, there might succeed love: and having been renewed into a new man, only in hope, not yet in substance, you learned how nothing of your good had preceded, and by the grace of God you were converted to God: now perchance since the time that you have been converted will you have anything of your own, and on your own strength ought thou to rely?
Just as men are wont to say, now leave me, it was necessary for you to show me the way; it is sufficient, I will walk in the way. And he that has shown you the way, “will you not that I conduct you to the place?” But you, if you are conceited, “let me alone, it is enough, I will walk in the way.” You are left, and through your weakness again you will lose the way. Good were it for you that He should have conducted you, who first put you in the way. But unless He too lead you, again also you will stray: say to Him then, “Conduct me, O Lord, in Your way, and I will walk in Your truth.” But your having entered on the way, is youth, the very renewal and beginning of the faith.
For before you were walking through your own ways a vagabond; straying through woody places, through rough places, torn in all your limbs, you were seeking a home, that is, a sort of settlement of your spirit, where you might say, it is well; and being in security might say it, at rest from every uneasiness, from every trial, in a word from every captivity; and thou did not find. What shall I say? Came there to you one to show you the way? There came to you the Way itself, and you were set therein by no merits of your preceding, for evidently you were straying.
What, since the time that you have set foot therein do you now direct yourself? Does He that has taught you the way now leave you? No, he says: “You have taught me from my youth; and even until now I will tell forth Your wonderful works.” For a wonderful thing is that which still You do; namely, that You direct me, who in the way has put me: and these are Your wonderful works. What do you think to be the wonderful works of God? What is more wonderful among God's wonderful works, than the raising the dead?
But am I by any means dead, you say? Unless dead you had been, there would not have been said to you, “Rise, you that sleepest, and arise from the dead, and Christ shall enlighten you.” Dead are all unbelievers, all unrighteous men; in body they live, but in heart they are extinct. But he that raises a man dead according to the body, does bring him back to see this light and to breathe this air: but he that raises is not himself light and air to him; he begins to see, as he saw before.
A soul is not so resuscitated. For a soul is resuscitated by God; though even a body is resuscitated by God: but God, when He does resuscitate a body, to the world does bring it back: when He does resuscitate a soul, to Himself He brings it back. If the air of this world be withdrawn, there dies body: if God be withdrawn, there dies soul. When then God does resuscitate a soul, unless there be with her He that has resuscitated, she being resuscitated lives not. For He does not resuscitate, and then leave her to live to herself: in the same manner as Lazarus, when he was resuscitated after being four days dead, was resuscitated by the Lord's corporal presence....The Lord withdrew from that same city or from that spot, did Lazarus cease to live?
Not so is the soul resuscitated: God does resuscitate her, she dies if God shall have withdrawn. For I will speak boldly, brethren, but yet the truth. Two lives there are, one of the body, another of the soul: as the life of the body is the soul, so the life of the soul is God: in like manner as, if the soul forsake, the body dies: so the soul dies, if God forsake. This then is His grace, namely, that He resuscitate and be with us. Because then He does resuscitate us from our past death, and does renew in a manner our life, we say to Him, “O God, You have taught me from my youth.”
But because He does not withdraw from those whom He resuscitates, lest when He shall have withdrawn from them they die, we say to Him, “and even until now I will tell forth Your wonderful works:” because while You are with me I live, and of my soul You are the life, which will die if she be left to herself. Therefore while my life is present, that is, my God, “even until now,” what next?
Source: The Enarrations, or Expositions, on the Psalms (New Advent)