10 Let us therefore, beloved, fear the hearing these words. Life is not a plaything: or rather our present life is a plaything, but the things to come are not such; or perchance our life is not a plaything only, but even worse than this. For it ends not in laughter, but rather brings exceeding damage on them who are not minded to order their own ways strictly. For what, I pray you, is the difference between children who are playing at building houses, and us when we are building our fine houses? What again between them making out their dinners, and us in our delicate fare? None, but just that we do it at the risk of being punished. And if we do not yet quite perceive the poverty of what is going on, no wonder, for we are not yet become men; but when we have become so, we shall know that all these things are childish.
For so those other things too, as we grow to manhood, we laugh to scorn; but when we are children we account them to be worth anxiety; and while we are gathering together potsherds and mire we think no less of ourselves than they who are erecting their great circuits of walls. Nevertheless they straightway perish and fall down, and not even when standing can they be of any use to us, as indeed neither can those fine houses. For the citizen of Heaven they cannot receive, neither can he bear to abide in them, who has his country above; but as we throw down these with our feet, so he too those by his high spirit. And as we laugh at the children, weeping at that overthrow, even so these also, when we are bewailing it all, do not laugh only, but weep also: because both their bowels are compassionate, and great is the mischief thence arising.
Let us therefore become men. How long are we to crawl on the earth, priding ourselves on stones and stocks? How long are we to play? And would we played only! But now we even betray our own salvation; and as children when they neglect their learning, and practise themselves in these things at their leisure, suffer very severe blows; even so we too, spending all our diligence herein, and having then our spiritual lessons required of us in our works, and not being able to produce them, shall have to pay the utmost penalty. And there is none to deliver us; though he be father, brother, what you will. But while these things shall all pass away, the torment ensuing upon them remains immortal and unceasing; which sort of thing indeed takes place with respect to the children as well, their father destroying their childish toys altogether for their idleness, and causing them to weep incessantly.
Source: Homilies on the Gospel of St. Matthew (New Advent)