The wondrous feeding of so many with so little echoes the manna in the Sinai desert, a theme which John will develop. As the waters under his feet obey him, so the waters of the Reed Sea obeyed Moses, allowing the Israelites to walk, if not on them, at least through them. Now John, the great dramatist, has set the stage for the main act. Let the play begin . Jesus has no illusions about their motives.
Eternal life is a major theme in John.
Here he connects it to bread, suggesting that just as the kind of bread they ate on the hillside the day before nourished their bodies in this temporal life, so the kind of bread he will provide will nourish their souls for eternal life. This type of progression is typical of John, and we'll see more of it. Probably plain old barley bread, the sort found on the humblest table every day. What it lacked in elegance, it made up for in nutrition. Unlike some of its delicate modern counterparts, it stuck to the ribs.