Cyprian

[One] will not be able to merit the mercy of God who himself has not been merciful, nor will [one] gain any request from the divine love by his prayers who has not been humane toward the prayer of the poor.

Treatise VIII. On Works and Alms 5 ↗

Augustine of Hippo

"Blessed is he that understandeth upon the needy and poor One: in the evil day shall the Lord deliver him" [Psalm 41:1]. For the evil day will come: will thou, hill thou, come it will: the Day of Judgment will come upon thee, an evil day if thou "understand not the needy and poor." For what now thou wilt not believe, shall be made manifest in the end. But neither shalt thou escape, when it shall be made manifest, because thou believest not, when it is kept secret. …

Exposition on Psalm 41 ↗

Ambrose of Milan

Faith comes first, and mercy comes second.… Happy, therefore, is the one who understands the poverty of Christ, his utter destitution. Christ, though he was very rich, became poor for us. In his kingdom, he was rich; in his flesh, he was poor, for he took on himself the flesh of the poor. We had indeed become very poor, because, by fraud practiced on us by the serpent, we lost the rich robes of virtue and were put out of paradise. We were thrown out of our native land and banished into exile. We were even stripped of clothing. …

Commentaries on the Twelve Davidic Psalms ↗

Thomas Aquinas

In the preceding Psalm, the Psalmist showed his confidence with respect to God; here, however, he asks from God a mercy that strengthens. The title is: "Unto the end, a Psalm of David." This title has already been explained above, namely that this Psalm which David composed leads us to the end, that is, to Christ, because it treats of his Passion with respect to certain things. …

Exposition on the Psalms of David ↗