Jerome
Catena Aurea · Matthäusevangelium 16
And when his disciples were come to the other side, they had forgotten to take bread. Then Jesus said unto them, Take heed and beware of the leaven of the Pharisees and of the Sadducees. And they reasoned among themselves, saying, It is because we have taken no bread. Which when Jesus perceived, he said unto them, O ye of little faith, why reason ye among yourselves, because ye have brought no bread? Do ye not yet understand, neither remember the five loaves of the five thousand, and how many baskets ye took up? Neither the seven loaves of the four thousand, and how many baskets ye took up? How is it that ye do not understand that I spake it not to you concerning bread, that ye should beware of the leaven of the Pharisees and of the Sadducees? Then understood they how that he bade them not beware of the leaven of bread, but of the doctrine of the Pharisees and of the Sadducees.
For he that takes heed of the leaven of the Pharisees and the Sadducees, does not observe the precepts of the Law and of the letter, and neglects the traditions of men that he may do the commandments of God. This is the leaven of which the Apostle speaks, A little leaven leaveneth the whole lump. (1 Cor. 5:6.) By every means also we should avoid that leaven which Marcion, Valentinus, and all the heretics had. For the nature of leaven is such, that when mixed with flour, that which seemed a little increases to a large quantity, and brings the whole mixture to its own flavour. Thus heretical doctrine if it have cast but a small spark into your breast, in a short time a mighty flame is raised, and drives the whole temper of the man along with it.