And when his disciples were come, &c.— This would be rendered more properly, Now the disciples, going to the other side, had forgotten to take bread; for it is more agreeable to the nature of the thing to suppose, that this conversation happened as they sailed, than when they were come to the other side, where they might easily have been supplied with bread. The version of 1729 renders it, Now at their departure to go to the other side, &c. And with it, Dr. Heylin and the Prussian editors agree. It seems Jesus and the disciples had remained so long in Dalmanutha, that they had consumed the seven baskets of fragments which they had taken up after the late miraculous dinner. Our Saviour hence took occasion to give his disciples a solemn charge to beware of the doctrine of the Pharisees and Sadducees, which he called leaven, because of its pernicious influence to sour men's tempers with pride and other evil passions. For as these hypocrites chiefly enjoined the observation of frivolous traditions, their doctrine was a great enemy to the principles of true piety, and puffed men up with a high conceit of their own sanctity. The slowness of the disciples' understanding shewed itself on this occasion, as it had done on many others. As they had forgotten to take bread with them, and had often heard the doctors prohibit the use of the leaven of heathens and Samaritans, they thought that he forbade them to buy bread from bakers of either sects, lest it might be made with impure leaven; and so they looked on the advice as an indirect reproof of their carelessness.
Our Saviour, after properly reproving them, soon gave them to understand his meaning. See Matthew 16:12. Mac-knight and Calmet.