9 But seeing, brethren, so long as “we are at home in this body, we are absent from the Lord;” and “the corruptible body presses down the soul, and the earthly tabernacle weighs down the mind that muses on many things;” even though we have some way or other dispersed the clouds, by walking as “longing” leads us on, and for a brief while have come within reach of that sound, so that by an effort we may catch something from that “house of God,” yet through the burden, so to speak, of our infirmity, we sink back to our usual level, and relapse to our ordinary state. And just as there we found cause for rejoicing, so here there will not be wanting an occasion for sorrow. For that hart that made “tears” its “bread day and night,” borne along by “longing to the water-brooks” (that is, to the spiritual delights of God), “pouring forth his soul above himself,” that he may attain to what is “above” his own soul, walking towards “the place of the wonderful tabernacle, even unto the house of God,” and led on by the sweetness of that inward spiritual sound to feel contempt for all outward things, and be borne on to things spiritual, is but a mortal man still; is still groaning here, still bearing about the frailty of flesh, still in peril in the midst of the “offenses” of this world. He therefore glances back to himself, as if he were coming from that world; and says to himself, now placed in the midst of these sorrows, comparing these with the things, to see which he had entered in there, and after seeing which he had come forth from thence;
“Why art you cast down, O my soul, and why do you disquiet me?”. Lo, we have just now been gladdened by certain inward delights: with the mind's eye we have been able to behold, though but with a momentary glance, something not susceptible of change: why do you still “disquiet me, why are you” still “cast down”? For you do not doubt of your God. For now you are not without somewhat to say to yourself, in answer to those who say, “Where is your God?” I have now had the perception of something that is unchangeable; why do you disquiet me still?
“Hope in God.” Just as if his soul was silently replying to him, “Why do I disquiet you, but because I am not yet there, where that delight is, to which I was, as it were, rapt for a moment? Am I already 'drinking' from this 'fountain' with nothing to fear?”...Still “Hope in God,” is his answer to the soul that disquiets him, and would fain account for her disquiet from the evils with which this world abounds. In the mean while dwell in hope: for “hope that is seen is not hope; but if we hope for that we see not, then do we with patience wait for it.”
Source: The Enarrations, or Expositions, on the Psalms (New Advent)