Hebrews 9:13-14
But perchance there are some persons so dissolute and silly as even during this very rebuke to laugh, because forsooth we thus discourse about laughter. For indeed such is their derangement, such their madness, that it does not feel the rebuke.
The Priest of God is Standing, offering up the prayer of all: and are you laughing, having no fears? And while he is offering up the prayers in trembling for you, do you despise all? Do you not hear the Scripture saying, “Woe, you despisers!”; do you not shudder? Do you not humble yourself? Even when you enter a royal palace, you order yourself in dress, and look, and gait, and all other respects: and here where there is the true Palace, and things like those of heaven, do you laugh? You indeed, I know, see [them] not, but hear thou that there are angels present everywhere, and in the house of God especially they stand by the King, and all is filled by those incorporeal Powers.
This my discourse is addressed to women also, who in the presence of their husbands indeed do not dare readily to do this, and even if they do it, it is not at all times, but during a season of relaxation, but here they do it always. Tell me, O woman, do you cover your head and laugh, sitting in the Church? Did you come in here to make confession of sins, to fall down before God, to entreat and to supplicate for the transgressions you have wretchedly committed, and do you do this with laughter? How then will you be able to propitiate Him?
9. But (one says) what harm is there in laughter? There is no harm in laughter; the harm is when it is beyond measure, and out of season. Laughter has been implanted in us, that when we see our friends after a long time, we may laugh; that when we see any persons downcast and fearful, we may relieve them by our smile; not that we should burst out violently and be always laughing. Laughter has been implanted in our soul, that the soul may sometimes be refreshed, not that it may be quite relaxed. For carnal desire also is implanted in us, and yet it is not by any means necessary that because it is implanted in us, therefore we should use it, or use it immoderately: but we should hold it in subjection, and not say, Because it is implanted in us, let us use it.
Serve God with tears, that you may be able to wash away your sins. I know that many mock us, saying, “Tears directly.” Therefore it is a time for tears. I know also that they are disgusted, who say, “Let us eat and drink, for tomorrow we die.” “Vanity of vanities, all is vanity.” It is not I that say it, but he who had had the experience of all things says thus: “I built for me houses, I planted vineyards, I made me pools of water, [I had] men servants and women servants.” And what then after all these things? “Vanity of vanities, all is vanity.”
Let us mourn therefore, beloved, let us mourn in order that we may laugh indeed, that we may rejoice indeed in the time of unmixed joy. For with this joy [here] grief is altogether mingled: and never is it possible to find it pure. But that is simple and undeceiving joy: it has nothing treacherous, nor any admixture. In that joy let us delight ourselves; that let us pursue after. And it is not possible to obtain this in any other way, than by choosing here not what is pleasant, but what is profitable, and being willing to be afflicted a little, and bearing all things with thanksgiving. For thus we shall be able to attain even to the Kingdom of Heaven, of which may we all be counted worthy, in Christ Jesus our Lord, with whom to the Father be glory, together with the Holy Ghost, now and for ever and world without end. Amen.
Source: Homilies on the Epistle to the Hebrews (New Advent)