Matthew 16:6

Herein the Apostles are admonished not to be partakers in the doctrine of the Jews; for the works of the Law were established to produce faith, and to prefigure the things that were to follow; and they on whose times truth itself had chanced should look for no further types of truth; lest the teaching of the Pharisees, which knew not of Christ, should stay the effect of Gospel truth.

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.

"And when His disciples," so it is said, "were come to the other side, they forgot to take bread. Then Jesus said unto them, Take heed and beware of the leaven of the Pharisees and of the Sadducees." And why said He not plainly, Beware of their teaching? His will is to remind them of what had been done, for He knew they had forgotten. But for accusing them at once there seemed to be no reasonable ground, but to take the occasion from themselves, and so to reprove them, would make the charge admissible. "And why did He not then reprove them, when they said, 'Whence should we have so many loaves in the wilderness?' for it seemed a good time then to say what He says here." That He might not seem to rush hastily on the miracle. And besides, He would not blame them before the multitude, nor seek honor in their presence. And now too the accusation had greater reason, for that after repetition of the miracle they were so minded.

They were bound to their Master with so great affection, that they were unwilling to part from Him for even a moment of time. And herein it should be observed how far they were from any longing for delicacies, when they took so small care for necessaries, that they had even forgotten to take bread, without which human weakness cannot support itself. He said unto them, Take heed and beware of the leaven of the Pharisees; and of the Sadducees.