26 Cry we therefore with the spirit of charity, and until we come to the inheritance in which we are always to remain, let us be, through love which becomes the free-born, not through fear which becomes bondmen, patient of suffering. Cry we, so long as we are poor, until we be with that inheritance made rich. Seeing how great earnest thereof we have received, in that Christ to make us rich made Himself poor; Who being exalted unto the riches which are above, there was sent One Who should breathe into our hearts holy longings, the Holy Spirit.
Of these poor, as yet believing, not yet beholding; as yet hoping, not yet enjoying; as yet sighing in desire, not yet reigning in felicity; as yet hungering and thirsting, not yet satisfied: of these poor, then, “the patience shall not perish for ever:” not that there will be patience there also, where anything to endure shall not be; but “will not perish,” meaning that it will not be unfruitful. But its fruit it will have for ever, therefore it “shall not perish for ever.” For he who labors in vain, when his hope fails for which he labored, says with good cause, “I have lost so much labor:” but he who comes to the promise of his labor says, congratulating himself, I have not lost my labor.
Labor then is said not to perish (or be lost), not because it lasts perpetually, but because it is not spent in vain. So also the patience of the poor of Christ (who yet are to be made rich as heirs of Christ) shall not perish for ever: not because there also we shall be commanded patiently to bear, but because for that which we have here patiently borne, we shall enjoy eternal bliss. He will put no end to everlasting felicity, Who gives temporal patience unto the will: because both the one and the other is of Him bestowed as a gift upon charity, Whose gift that charity is also.
Source: On Patience (New Advent)