13 “And the Heaven shall declare His righteousness”. Truly this righteousness of God to us the “heavens have declared,” the Evangelists have foretold. Through them we have heard that some will be on the right hand, to whom the Householder says, “Come, you blessed of My Father, receive.” Receive what? “A kingdom.” In return for what thing? “I was an hungred, and you gave Me to eat.” What so valueless, what so earthly, as to break bread to the hungry? At so much is valued the kingdom of heaven.
“Break your bread to the hungry, and the needy without covering bring into your house; if you see one naked, clothe him.” If you have not the means of breaking bread, hast not house into which you may bring, hast not garment wherewith you may cover: give a cup of cold water, cast two mites into the treasury. As much the widow does buy with two mites, as Peter buys, by leaving the nets, as Zacchæus buys by giving half his goods. Of so much worth is all that you have. “The heavens shall declare His righteousness, for God is Judge.”
Truly judge not confounding but severing. For “the Lord knows them that are His.” Even if grains lie hidden in the chaff, they are known to the husbandman. Let no one fear that he is a grain even among the chaff; the eyes of our winnower are not deceived. Fear not lest that tempest, which shall be round about Him, should confound you with chaff. Certainly mighty will be the tempest; yet not one grain will it sweep from the side of the grain to the chaff: because not any rustic with three-pronged fork, but God, Three in One, is Judge.
And the heavens shall declare His righteousness: for God is Judge. Let heavens go, let the heavens tell, into every land let their sound go out, and unto the ends of the world their words: and let that body say, “From the ends of the world unto You have I cried, when my heart was in heaviness.” For now mingled it groans, divided it shall rejoice. Let it cry then and say, “Destroy not my soul with ungodly men, and with men of blood my life.” He destroys not together, because God is Judge. Let it cry to Him and say, “Judge me, O Lord, and sever my cause from the nation unholy:” let it say, He shall do it: there shall be gathered to Him His righteous ones. He has called the earth that He may sever His people.
Source: The Enarrations, or Expositions, on the Psalms (New Advent)