Charles Ellicott Commentary Mark 8:15

"And he charged them, saying, Take heed, beware of the leaven of the Pharisees and the leaven of Herod." — Mark 8:15 (ASV)

He charged them.—The verb is in the imperfect tense, and implies that the command was repeated more than once. Therefore they, too, “were reasoning,” more than once, what was the meaning of the precept on which so much stress was placed.

The leaven of Herod.—The words imply the presence among the questioners of Mark 8:11 of others besides the Pharisees. On the connection between the “leaven of Herod” and that of “the Sadducees” in Matthew 16:6, see Note on that verse.