30 “Poor and sorrowful I am”. Why this? Is it that we may acknowledge that through bitterness of soul this poor One does speak evil? For He has spoken of many things to happen to them. And as if we were saying to Him, “Why such things?”— “Nay, not so much!” He answers, “poor and sorrowful I am.” They have brought Me to want, unto this sorrow they have set Me down, therefore I say these words. It is not, however, the indignation of one cursing, but the prediction of one prophesying.
For He was intending to recommend to us certain things which hereafter He says of His poverty and His sorrow, in order that we may learn to be poor and sorrowful. For, “Blessed are the poor, for theirs is the kingdom of Heaven.” And, “Blessed are they that mourn, for they shall be comforted.” This therefore He does Himself before now show to us: and so, “poor and sorrowful I am.” The whole Body of Him says this. The Body of Christ in this earth is poor and sorrowful. But let Christians be rich.
Truly if Christians they are, they are poor; in comparison with the riches celestial for which they hope, all their gold they count for sand. “And the health of Your countenance, O God, has taken Me up.” Is this poor One anywise forsaken? When do you deign to bring near to your table a poor man in rags? But again, this poor One the health of the countenance of God has taken up: in His countenance He has hidden His need. For of Him has been said, “You shall hide them in the hiding place of Your countenance.” But in that countenance what riches there are would ye know?
Riches here give you this advantage, that you may dine on what you will, whenever you will: but those riches, that you may never hunger. “The health of Your countenance, O God, has taken Me up.” For what purpose? In order that no longer I may be poor, no longer sorrowful? “I will praise the name of the Lord with a song, I will magnify Him in praise”. Now it has been said, this poor One praises the name of the Lord with a song, he magnifies Him in praise. When would He have ventured to sing, unless He had been refreshed from hunger?
“I will magnify Him with praise.” O vast riches! What jewels of God's praise has he brought out of his inward treasures! These are my riches! “The Lord has given, the Lord has taken away.” Then miserable he has remained? Far be it. See the riches: “As it has pleased the Lord, so has been done, be the name of the Lord blessed.”
Source: The Enarrations, or Expositions, on the Psalms (New Advent)