As a skilful physician from the colour of the skin infers the sick man’s disease, so John understood the evil thoughts of the Pharisees who came to him. They thought perhaps, We go, and confess our sins; he imposes no burden on us, we will be baptized, and get indulgence for sin. Fools! if ye have eaten of impurity, must ye not needs take physic? So after confession and baptism, a man needs much diligence to heal the wound of sin; therefore he says, “Generation of vipers.”
It is the nature of the viper as soon as it has bit a man to fly to the water, which, if it cannot find it, straightway dies; so this “progeny of vipers,” after having committed deadly sin, ran to baptism, that, like vipers, they might escape death by means of water.
Moreover it is the nature of vipers to burst the insides of their mothers, and so to be born. The Jews then are therefore called “progeny of vipers,” because by continual persecution of the prophets they had corrupted their mother the Synagogue. Also vipers have a beautiful and speckled outside, but are filled with poison within. So these men’s countenances wore a holy appearance.
Reproduced in full. Translation: Oxford 1841 (Newman), public domain (Public domain).