2 Let us then, as is becoming, as at all times, yet especially in the days of the feast, be not hearers only, but doers of the commandments of our Saviour; that having imitated the behaviour of the saints, we may enter together into the joy of our Lord which is in heaven, which is not transitory, but truly abides; of which evil doers having deprived themselves, there remains to them as the fruit of their ways, sorrow and affliction, and groaning with torments. Let a man see what these become like, that they bear not the likeness of the conversation of the saints, nor of that right understanding, by which man at the beginning was rational, and in the image of God. But they are compared to their disgrace to beasts without understanding, and becoming like them in unlawful pleasures, they are spoken of as wanton horses; also, for their craftiness, and errors, and sin laden with death, they are called a 'generation of vipers,' as John says. Now having thus fallen, and grovelling in the dust like the serpent, having their minds set on nothing beyond visible things, they esteem these things good, and rejoicing in them, serve their own lusts and not God.
Source: Letters (New Advent)