For it is shewn by the unchangeableness of the Divine sentence, that no aid of mercy can be rendered to men by the righteous, even though they should wish to give it; by which he reminds us, that in this life men should relieve those they can, since hereafter even if they be well received, they would not be able to give help to those they love. For that which was written, that they may receive you into everlasting habitations, was not said of the proud and unmerciful, but of those who have made to themselves friends by their works of mercy, whom the righteous receive, not as if by their own power benefitting them, but by Divine permission.
Reproduced in full. Translation: Oxford 1841 (Newman), public domain (Public domain).
Also cites: Qu. Ev. lib. ii. qu. 88.