The two verbs of warning, Take heed … beware, each have their distinct original meaning and history of usage, but in this context they mean essentially the same thing. Die Bibel im heutigen Deutsch places the two verbs together in the construction “Be on your guard against….” “Watch out for” and “Be careful” are other appropriate warnings.

In place of the leaven of the Pharisees and Sadducees, Mark has “the leaven of the Pharisees and the leaven of Herod” (8.15), while in another context Luke has “the leaven of the Pharisees, which is hypocrisy” (12.1). Moreover, where Matthew explains the meaning of leaven (verse 12), Mark leaves his readers to draw their own conclusions. Although Jesus here uses leaven (Good News Translation “yeast”) figuratively, its significance must not be explained in translation until verses 11-12, the place in the narrative where the explanation is given. Otherwise the astonishment of the disciples will make absolutely no sense.

Leaven or “yeast” is not known in many parts of the world, but there are sometimes other types of fermenting agents that can serve as an equivalent. Translators can then say “fermenting agent for bread (or, dough).” For example, in parts of Africa where beer is commonly brewed from grain, the froth on top contains the fermenting agent, and some of it can be preserved as a starter for the next batch. Translators in those areas have sometimes said “substance like beer froth that makes bread dough rise.” In other cases, where the fermentation process is even less well understood, translators have used a functional description such as “substance that spoils (or raises, or causes to rise) the dough so you can make bread from it.” To simply borrow the word leaven or “yeast” would not help here, since it is the fermenting or spoiling process that is in focus. See also comments at 13.33.

The yeast is of the Pharisees and Sadducees, that is, “the yeast they use.” It is extending the image too far to believe that the reference is to something spoiled inside them.

Quoted with permission from Newman, Barclay M. and Stine, Philip C. A Handbook on the Gospel of Matthew. (UBS Handbook Series). New York: UBS, 1988. For this and other handbooks for translators see here .