‘In the mean time, when the many thousands of the multitude were gathered together, insomuch that they trod one on another, he began to say to his disciples first of all, “Beware you of the leaven of the Pharisees, which is hypocrisy.” '
Great crowds continued to gather (‘thousands of them') so much so that they were treading on one another, but Jesus had now begun primarily to teach His disciples, although undoubtedly keeping the wider crowd in mind. He warned them to “Beware of the leaven (or ‘yeast') of the Pharisees, which is hypocrisy.” Leaven was the old dough retained from bread-making which was allowed to ferment. It would then be put into the new dough to cause fermentation, so improving its structure and taste. Its effects would spread all the way through the new dough. It can therefore refer to any pervasive influence, whether good or bad, which can be introduced into something and then spread and spread.
In Luke 13:21; Matthew 13:33 leaven refers to the pervasive influence of the message of the Kingly Rule of God which spreads and spreads until it has reached everywhere. In Matthew 16:6; Matthew 16:11-12; Mark 8:15 it refers to the teaching of the Scribes and Pharisees, and of Herod, which could have a wrong pervasive influence, if His disciples were not wary. Indeed it could spoil their whole lives. In 1 Corinthians 5:6-7; Galatians 5:9 it refers to sin's pervasive influence in people's lives. It will be seen from this that leaven refers to influence that spread and spreads, whether good or bad. Because the influence mentioned elsewhere is bad, some even see the leaven which is revealed as pervading the Kingly Rule of God (Luke 13:21) as being bad as well, and as reflecting those who have failed to take heed to His warning against the leaven of the Pharisees, but if so it is not apparent from the context.
Here, however, it refers to the danger of taking up the hypocritical ways of the Scribes and Pharisees as outlined in Luke 11:37-53. They must neither copy their ways, nor let a similar attitude affect the way that they live their own lives. They must ensure that they are always open, straight and honest, and genuinely concerned for the good of others, seeking to submit themselves to the Kingly Rule of God in all humility, and not posturing or seeking honour and flattery.
We should recognise that they had been brought up all their lives to give deep respect to the Scribes and Pharisees, who were looked on as the very heart of Israel's spiritual life. Now they were to see their bad points, and not be too carried away by their ideas. They were to learn to discern. (They had no doubt already been greatly shocked to discover that these men did not see eye to eye with their Master).
‘Hypocrisy.' The word signifies play-acting and indicates those who put on a show on the outside which does not conform to what they are like inside, or those who say one thing and do another.