7 This man was baptizing in Jordan, and there went out unto him all Jerusalem, to enjoy the first-fruits of baptisms: for in Jerusalem is the prerogative of all things good. But learn, O you inhabitants of Jerusalem, how they that came out were baptized by him: confessing their sins, it is said. First they showed their wounds, then he applied the remedies, and to them that believed gave redemption from eternal fire. And if you will be convinced of this very point, that the baptism of John is a redemption from the threat of the fire, hear how he says, O generation of vipers, who has warned you to flee from the wrath to come ? Be not then henceforth a viper, but as you have been formerly a viper's brood, put off, says he, the slough of your former sinful life. For every serpent creeps into a hole and casts its old slough, and having rubbed off the old skin, grows young again in body. In like manner enter thou also through the strait and narrow gate: rub off your former self by fasting, and drive out that which is destroying you. Put off the old man with his doings, and quote that saying in the Canticles, I have put off my coat, how shall I put it on?
But there is perhaps among you some hypocrite, a man-pleaser, and one who makes a pretence of piety, but believes not from the heart; having the hypocrisy of Simon Magus; one who has come hither not in order to receive of the grace, but to spy out what is given: let him also learn from John: And now also the axe is laid unto the root of the trees, Every tree therefore that brings not forth good fruit is hewn down, and cast into the fire. The Judge is inexorable; put away your hypocrisy.
Source: Catechetical Lectures (New Advent)