beware of the leaven. Figure of speech Hypocatastasis. leaven put by implication for "doctrine" (Mat_16:12), because of its evil effects. Compare notes on Mat_15:26, and Mat_13:33.
beware = pay attention to, so as to be careful of.
of = from. Here, away from: i.e. beware [and keep] away from, or keep clear of, as in Mat_7:15. Greek. apo.App-104.