From: John 6:22-29
The People Look for Jesus
 On the next day the people who remained on the other side of the sea saw that there had been only one boat there, and that Jesus had not entered the boat with His disciples, but that His disciples had gone away alone.  However, boats from Tiberias came near the place where they ate the bread after the Lord had given thanks.  So when the people saw that Jesus was not there, nor His disciples, they themselves got into the boats and went to Capernaum, seeking Jesus.
The Discourse on the Bread of Life
 When they found Him on the other side of the sea, they said to Him, "Rabbi, when did You come here?"  Jesus answered them, "Truly, truly, I say to you, you seek Me, not because you saw signs, but because you ate your fill of the loaves.  Do not labor for the food which perishes, but the food which endures to eternal life, which the Son of Man will give to you; for on Him has God the Father set His seal."  Then they said to Him, "What must we do, to be doing the works of God?"  Jesus answered them, "This is the work of God, that you believe in Him He has sent."
26. Our Lord begins by pointing out that their attitudes are wrong: if they have the right attitude they will be able to understand His teaching in the eucharistic discourse. "You seek me", St. Augustine comments, "for the flesh, not for the spirit. How many seek Jesus for no other purpose than that He may do them good in this present life! [...] Scarcely ever is Jesus sought for Jesus' sake" ("In Ioann.
Evang.", 25, 10).
This verse marks the beginning of the discourse on the bread of life which goes up to verse 59. It opens with an introduction in the form of a dialogue between Jesus and the Jews (verses 26-34), in which our Lord reveals Himself as the bringer of the messianic gifts. Then comes the first part of the discourse (verses 35-47), in which Jesus presents Himself as the Bread of Life, in the sense that faith in Him is food for eternal life. In the second part (verses 48-59) Christ reveals the mystery of the Eucharist: He is the Bread of Life who gives Himself sacramentally as genuine food.
27. Bodily food helps keep us alive in this world; spiritual food sustains and develops supernatural life, which will last forever in Heaven. This food, which only God can give us, consists mainly in the gift of faith and sanctifying grace. Through God's infinite love we are given, in the Blessed Eucharist, the very author of these gifts, Jesus Christ, as nourishment for our souls.
"On Him has God the Father set His seal": our Lord here refers to the authority by virtue of which He can give men the gifts He has referred to: for, being God and man, Jesus' human nature is the instrument by means of which the Second Person of the Blessed Trinity acts. St. Thomas Aquinas comments on this sentence as follows: "What the Son of Man will give He possesses through His superiority over all other men in His singular and outstanding fullness of grace. ...When a seal is impressed on wax, the wax receives the complete form of the seal. So it is that the Son received the entire form of the Father. This occurred in two ways; eternally (eternal generation), which is not referred to here because the seal and the sealed are different in nature from one another; what is referred to here is the other manner, that is, the mystery of the Incarnation, whereby God the Father impressed on human nature the Word, who is the reflection and the very stamp of God's nature, as Hebrews 1:3 says" ("Commentary on St. John, in loc.").
Source: "The Navarre Bible: Text and Commentaries". Biblical text taken from the Revised Standard Version and New Vulgate. Commentaries made by members of the Faculty of Theology of the University of Navarre, Spain. Published by Four Courts Press, Kill Lane, Blackrock, Co. Dublin, Ireland. Reprinted with permission from Four Courts Press and Scepter Publishers, the U.S. publisher.