“But when he saw many of the Pharisees and Sadducees come to his baptism, he said unto them, O generation of vipers, who hath warned you to flee from the wrath to come?”
Matthew 3:7 — Greek Interlinear
Church Fathers on Matthew 3:7
The words of the teachers should be fitted to the quality of the hearers, that in each particular it should agree with itself and yet never depart from the fortress of general edification.
It was necessary that after the teaching which he used to the common people, the Evangelist should give an example of the doctrine he delivered to the more advanced; therefore he says, 'Seeing many of the Pharisees, &c.'
The manner of Scripture is to give names from the imitation of deeds, according to that of Ezekiel, 'Thy father was an Amorite;' [Ezek 16:3] so these from following vipers are called 'generation of vipers.'