Matthew 16:6 - Ellicott's Commentary On The Whole Bible

Beware of the leaven of the Pharisees. — The form of the warning was obviously determined by the fact just narrated. The Master saw the perplexed looks and heard the self reproaching or mutually accusing whispers of the disciples, and made them the text of a proverb which was a concentrated parable. As St. Mark gives the words, they stand, “Beware of the leaven of the Pharisees, and of the leaven of Herod,” and this, if we have to make our choice, we may believe to have been the form in which they were actually spoken; St. Matthew, or the report which he followed, substituting for the less known Herodians the better known Sadducees. The language of the tetrarch, as has been shown (see Note on Matthew 14:2), implies that Sadduceeism had been the prevailing belief of his life, and the current of Jewish political, not to say religious, sympathies, naturally led the Sadducean priests, courting (as Caiaphas did) the favour of the Roman rulers, to fraternise with the scribes who attached themselves to the party of the tetrarch. (Comp. Acts 5:17.)