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.”
[AD 397] Ambrose of Milan on Psalms 63:5-9