8 And this I say, not that we may omit supplicating the saints, but to hinder our being careless, and entrusting our concerns to others only, while we fall back and slumber ourselves. For so when He said, “make to yourselves friends,” he did not stop at this only, but He added, “of the unrighteous mammon;” that so again the good work may be your own; for it is nothing else but almsgiving which He has here signified. And, what is marvellous, neither does He make a strict account with us, if we withdraw ourselves from injustice.
For what He says is like this: “Have you gained ill? Spend well. Have you gathered by unrighteousness? Scatter abroad in righteousness.” And yet, what manner of virtue is this, to give out of such gains? God, however, being full of love to man, condescends even to this and if we thus do, promises us many good things. But we are so past all feeling, as not to give even of our unjust gain, but while plundering without end, if we contribute the smallest part, we think we have fulfilled all.
Have you not heard Paul saying, “He which sows sparingly, shall reap also sparingly”? Wherefore then do you spare? What, is the act an outlay? Is it an expense? Nay, it is gain and good merchandise. Where there is merchandise, there is also increase; where there is sowing, there is also reaping. But you, if you had to till a rich and deep soil, and capable of receiving much seed, would both spend what you had, and would borrow of other men, accounting parsimony in such cases to be loss; but, when it is Heaven which you are to cultivate, which is exposed to no variation of weather, and will surely repay your outlay with abundant increase, you are slow and backward, and considerest not that it is possible by sparing to lose, and by not sparing to gain.
Source: Homilies on the Gospel of St. Matthew (New Advent)