John 6:12

When they were filled
Had not only eaten, but had made a full meal, and were thoroughly satisfied, having eaten as much as they could, or chose to eat:

he said unto his disciples, gather up the fragments that remain,
that nothing be lost;
this he said, partly that the truth, reality, and greatness of the miracle might be clearly discerned; and partly, to teach frugality, that, in the midst of abundance, care be taken that nothing be lost of the good things which God gives; and which may be useful to other persons, or at another time.