The Pulpit Commentary - Matthew 16:12
Then understood they. Jesus did not explain his meaning further; but his reproof roused their intellect, made them reflect, set them on the road to the truth. The doctrine. This was what Jesus meant by "the leaven." In a wider sense it might include practice as well as precept, manner of life as well as teaching. The same spirit permeated all. "See," says St. Chrysostom, "how much good his reproof wrought. For it both led them away from the Jewish observances, and, when they were remiss.... read more
The Pulpit Commentary - Matthew 16:11
That I spake it not to you, etc. The Revised Version, following many modern editors, divides the clause into two, thus: that I spake not to you concerning bread? But beware of the leaven, etc. This is the second ground for the Lord's reproof administered to the apostles. They had taken in a carnal, literal sense a word which he had used in a symbolical or mystical meaning. It is the want of spiritual discernment which he censures. They had had frequent opportunities of hearing and... read more