John Calvin on John 7:20

20. Thou hast a devil. The meaning is, “Thou art mad;” for it was a customary phrase among the Jews, who had been trained to the doctrine that, when men are excited to rage, or when they have lost sense and reason, they are tormented by the devil. And, indeed, as gentle and moderate chastisements are God’s fatherly rods, so when He treats us with greater harshness and severity, He appears not to strike us with his own hand, but rather to employ the devil as the executioner and minister of his wrath. Again, the multitude reproach Christ with simplicity; for the common people were not acquainted with the intentions of the priests. Those foolish men, therefore, ascribe it to madness, when Christ complains that they are endeavoring to put him to death. We learn from it that we ought to be exceedingly cautious not to form an opinion about subjects which we do not understand; but, if it ever happens that we are rashly condemned by ignorant men, mildly to digest such an affront.