“But I”. I for whom they were seeking evil, I whose “life they were seeking, that they might take it away.” But turn you to another description of persons. But I to whom they said, “Well done! Well done!” “I am poor and needy.” There is nothing in me that may be praised as my own. Let Him rend my sackcloth in sunder, and cover me with His robe. For, “Now I live, not I myself; but Christ lives in me.” If it is Christ that “lives in you,” and all that you have is Christ's, and all that you are to have hereafter is Christ's also; what are you in yourself? “I am poor and needy.” Now I am not rich, because I am not proud. He was rich who said, “Lord, I thank You that I am not as other men are;” but the publican was poor, who said, “Lord, be merciful to me a sinner!” The one was belching from his fullness; the other from want was crying piteously, “I am poor and needy!” And what would you do, O poor and needy man? Beg at God's door; “Knock, and it shall be opened unto you.” — “As for me, I am poor and needy. Yet the Lord cares for me.”— “Cast your care upon the Lord, and He shall bring it to pass.” What can you effect for yourself by taking care what can you provide for yourself? Let Him who made you “care for you.” He who cared for you before thou were, how shall He fail to have a care of you, now that you are what He would have you be? For now you are a believer, now you are walking in the “way of righteousness.” Shall not He have a care for you, who “makes His sun rise on the good and on the evil, and sends rain on the just and on the unjust”?...
“You are my Help, and my Deliverer; make no tarrying, O my God”. He is calling upon God, imploring Him, fearing lest he should fall away: “Make no tarrying.” What is meant by “make no tarrying”? We lately read concerning the days of tribulation: “Unless those days should be shortened, there should no flesh be saved.” The members of Christ— the Body of Christ extended everywhere— are asking of God, as one single person, one single poor man, and beggar! For He too was poor, who “though He was rich, yet became poor, that you through His poverty might be made rich.” It is He that makes rich those who are the true poor; and makes poor those who are falsely rich. He cries unto Him; “From the end of the earth I cried unto You, when my heart was in heaviness.” There will come days of tribulations, and of greater tribulations; they will come even as the Scripture speaks: and as days advance, so are tribulations increased also. Let no one promise himself what the Gospel does not promise....
Source: The Enarrations, or Expositions, on the Psalms (New Advent)