John Calvin Commentary Matthew 14:20

"And they all ate, and were filled: and they took up that which remained over of the broken pieces, twelve baskets full." — Matthew 14:20 (ASV)

And carried away what was left. The fragments that remained after satisfying so great a multitude of people were more than twelve times larger in quantity than what was at first put into their hands, and this contributed not a little to the splendor of the miracle. In this way, all came to know that the power of Christ had not only created out of nothing the food that was necessary for immediate use, but that, if it should be required, there was also provision for future needs. In short, Christ intended that, after the miracle had been performed, a striking proof of it should still remain, which, after being refreshed by food, they might contemplate at leisure.

Now, though Christ does not every day multiply our bread or feed people without the labor of their hands or the cultivation of their fields, the benefit of this narrative extends even to us. If we do not perceive that it is the blessing of God that multiplies the grain, so that we may have a sufficiency of food, the only obstacle is our own indolence and ingratitude. That seed remains for the following year after we have been supported by the annual produce, and that this could not have happened without an increase from heaven, each of us would easily perceive, if he were not hindered by that very depravity which blinds the eyes of both the mind and the flesh, so that he does not see a manifest work of God. Christ intended to declare that, as all things have been delivered into his hands by the Father, so the food we eat proceeds from his grace.