Where does the prodigal son realize he can go for sustenance?
The prodigal son realizes he can go only back to the Father for sustenance and spiritual life. He recognizes his need, that he must return to the Giver of the covenant promises. So he comes back to the Father, the only one who can fill him.
Les explains that the youngest son, like the one little lamb caught in the thicket, realizes his need and that there is only one place he can go for sustenance—back to the Father. He must return to the Giver of covenant promises and spiritual life. This illustrates the point of Jesus' parables to Israel: they needed Him, and the signs in John had a specific message for the nation, showing they needed the One who could fill them. Les also notes that most sermons omit the elder brother, but he addresses him because he fits the story, as seen when the elder son was in the field and heard music and dancing.