Now let us turn our attention to the characteristic of fatness or richness of which David speaks intelligibly when he says, “Let my soul be filled as with marrow and fatness.” Before that he had said, “And may your whole burnt offering be made fat.” By this he means that the requirements for a sacrifice are that it be fat or rich, that it be glistening and that it be weighted with the sustenance inspired by faith and devotion and by the rich nourishment of the Word of God. Frequently we use the word fat or rich when we refer to something that is heavily and elaborately adorned, and to the finest victim as one that is not thin and scrawny. Wherefore we designate as “rich” a sacrifice that we desire to be regarded as the “finest.” We also have proof of this when we consult the prophetic passage in the Scriptures where fine cows are compared with years of fertility!
Why do we forget about wickedness? It is due to our remembrance of good things, due to our remembrance of God. If we continually remember God, we cannot remember those things also. For [he says], “When I remembered you on my bed, I thought on you in the morning dawn.” We ought then to have God always in remembrance, but then especially, when thought is undisturbed, when by means of that remembrance [one] is able to condemn himself, when he can retain [things] in memory. For in the daytime indeed, if we do remember, other cares and troubles entering in, drive the thought out again; but in the night it is possible to remember continually, when the soul is calm and at rest; when it is in the heaven, and under a serene sky. “The things that you say in your hearts you should grieve over on your beds,” he says. For it was indeed right to remember this throughout the day also. But inasmuch as you are always full of cares and distracted amid the things of this life, at least then remember God on your bed; at the morning dawn meditate on him.
Pure prayer such as is worthy of God, O disciple of God, is not uttered by means of compound words. Prayer that is worthy of God consists in this: that one gather in one’s mind from the entire world and not let it be secretly bound to anything; that one place it entirely at God’s disposal and forget, during the time of prayer, everything that is material, including one’s own self and the place where one is standing. One should be secretly swallowed up in the spirit of God, and one should clothe oneself in God at the time of prayer both outwardly and inwardly, set on fire with ardent love for him and entirely engulfed in his thoughts of God, entirely commingled in all of him, with the movements of one’s thoughts suffused with wondrous recollection of God, while the soul has gone out in love to seek him whom it loves, just as David said, “My soul has gone out after you.”
"If I have remembered You upon my bed, in the dawnings I did meditate on you [Psalm 63:7]: because You have become my helper" [Psalm 63:8]. His "bed" he calls his rest. When any one is at rest, let him be mindful of God; when any one is at rest, let him not by rest be dissolved, and forget God: if mindful he is of God when he is at rest, in his actions on God he does meditate. For the dawn he has called actions, because every man at dawn begins to do something. What therefore has he said? If therefore I was not mindful on my bed, in the dawn also I did not meditate on You. Can he that thinks not of God when he is at leisure, in his actions think of God? But he that is mindful of Him when he is at rest, on the Same does meditate when he is doing, lest in action he should come short. Therefore he has added what? "Because You have become my helper." For unless God aid our good works, they cannot be accomplished by us. And worthy things we ought to work: that is, as though in the light, since by Christ showing the way we work. Whosoever works evil things, in the night he works, not in the dawn; according to the Apostle, saying, "They that are drunken, in the night are drunken; and they that sleep, in the night do sleep; let us that are of the day, be sober." [1 Thessalonians 5:7-8] He exhorts us that after the day we should walk honestly: "As in the day, honestly let us walk." [Romans 13:13] And again, "You," he says, "are sons of light, and sons of day; we are not of night nor of darkness." [1 Thessalonians 5:5] Who are sons of night, and sons of darkness? They that work all evil things. To such a degree they are sons of night, that they fear lest the things which they work should be seen....No one therefore in the dawn works, except him that in Christ works. But he that while at leisure is mindful of Christ, on the Same does meditate in all his actions, and He is a helper to him in a good work, lest through his weakness he fail. "And in the covering of Your wings I will exult." I am cheerful in good works, because over me is the covering of Your wings. If you protect me not, forasmuch as I am a chicken, the kite will seize me. For our Lord Himself says in a certain place to that Jerusalem, a certain city, where He was crucified: "Jerusalem," He says, "Jerusalem, how often I have willed to gather your sons, as though a hen her chickens, and you would not." [Matthew 23:37] Little ones we are: therefore may God protect us under the shadow of His wings. What when we shall have grown greater? A good thing it is for us that even then He should protect us, so that under Him the greater, always we be chickens. For always He is greater, however much we may have grown. Let no one say, let Him protect me while I am a little one: as if sometime he would attain to such magnitude, as should be self-sufficient. Without the protection of God, nought you are. Alway by Him let us desire to be protected: then always in Him we shall have power to be great, if always under Him little we be. "And in the covering of Your wings I will exult."
[AD 397] Ambrose of Milan on Psalms 63:5-9