2 “Blessed is he that understands upon the needy and poor One: in the evil day shall the Lord deliver him”. For the evil day will come: will thou, nill thou, come it will: the Day of Judgment will come upon you, an evil day if you “understand not the needy and poor.” For what now you will not believe, shall be made manifest in the end. But neither shall you escape, when it shall be made manifest, because you believe not, when it is kept secret. Invited are you, what you see not to believe, lest when thou see, thou be put to the blush.
“Understand then upon the needy and poor One,” that is, Christ: understand in Him the hidden riches, whom poor you see, “In Him are hid all the treasures of wisdom and knowledge.” For thereby in the evil day shall He deliver you, in that He is God: but in that He is man, and that which in Him is human has raised to life, and changed for the better, He has lifted (you) to heaven. But He who is God, who would have one person in man and with man, could neither decrease nor increase, neither die nor rise again.
He died out of man's infirmity, but God dies not....But as we rightly say, Such a man died, though his soul dies not; so we rightly say, Christ died, though His Divinity dies not. Wherefore died? Because needy and poor. Let not His death offend you, and avert you from beholding His Divinity. “Blessed is he that understands upon the needy and poor One.” Consider also the poor, the needy, the hungry and thirsty, the naked, the sick, the prisoners; understand also upon such poor, for if upon such thou understand, you understand upon Him who said, “I was an hungred, I was thirsty, I was a stranger, naked, sick, in prison;” so in the evil day shall the Lord deliver you....
Source: The Enarrations, or Expositions, on the Psalms (New Advent)