But do you desire glory? Does not then that suffice you which is given by the receiver himself, that from our gracious God, but do you set your heart on that from men also? Take heed, lest you undergo the contrary, lest some condemn you as not showing mercy, but making a display, and seeking honor, as making a show of the calamities of others.
For indeed the showing of mercy is a mystery. Shut therefore the doors, that none may see what it is not pious to display. For our mysteries too are above all things, a showing of God's mercy and loving-kindness. According to His great mercy, He had mercy on us being disobedient.
And the first prayer too is full of mercy, when we entreat for the energumens; and the second again, for others under penance seeking for much mercy; and the third also for ourselves, and this puts forward the innocent children of the people entreating God for mercy. For since we condemn ourselves for sins, for them that have sinned much and deserve to be blamed we ourselves cry; but for ourselves the children; for the imitators of whose simplicity the kingdom of heaven is reserved. For this image shows this, that they who are like those children, lowly and simple, these above all men are able to deliver the guilty by their prayers.
But the mystery itself, of how much mercy, of how much love to man it is full, the initiated know.
Do thou then, when according to your power you are showing mercy to a man, shut the doors, let the object of your mercy see it only; but if it be possible, not even he. But if you set them open, you are profanely exposing your mystery.
Consider that the very person, whose praise you seek, even himself will condemn you; and if he be a friend, will accuse you to himself; but if an enemy, he will deride you unto others also. And you will undergo the opposite of what you desire. For thou indeed desirest that he should call you the merciful man; but he will not call you this, but the vainglorious, the man-pleaser, and other names far more grievous than these.
But if you should hide it, he will call you all that is opposite to this; the merciful, the kind. For God suffers it not to be hidden; but if you conceal it, the other will make it known, and greater will be the admiration, and more abundant the gain. So that even for this very object of being glorified, to make a display is against us; for with respect to the thing unto which we most hasten and press, as to this most especially is this thing against us. For so far from obtaining the credit of being merciful, we obtain even the contrary, and besides this, great is the loss we undergo.
For every motive then let us abstain from this, and set our love on God's praise alone. For thus shall we both attain to honor here, and enjoy the eternal blessings, by the grace and love towards man of our Lord Jesus Christ, to whom be glory and might world without end. Amen.
Source: Homilies on the Gospel of St. Matthew (New Advent)