There are two additional aspects to the sacramental nature of the Bread of Life Discourse which are not brought out in other answers:
- Jesus is the one who provides the Bread.
- The inefficacy of the meal without belief.
The One Who Provides the Bread
J. H. Bernard saw the discourse as composed of three sections. In the third Jesus promises He will give bread in the future which the early church understood as sacramental feeding:
The first section tells of the Bread from heaven which God gives to those who believe in Jesus, and it announces that Jesus is, Himself, the Bread of Life. The second section is introduced by objections raised by "the Jews," and speaks further of Jesus as the Bread of Life, but does not say explicitly that this Bread is the gift of the Father...In the third section the terminology is changed, and not only the terminology but the doctrine as well. For Jesus speaks now, not of Himself as the heavenly Bread continually given by the Father to believers, but of the Bread which He is, Himself, to give them in the future (δώσω, v. 51). This gift is described as His flesh and His blood, which He will give for the life of the world, and which when appropriated by the believer will be the source and the guarantee of eternal life.1
No one would deny that there may be ways of "eating the flesh and drinking the blood" of Christ in a spiritual manner which do not involve sacramental feeding. But the language is sacramental, and was so understood throughout the second century.2
The initial act of providing Himself as bread came at the Last Supper. When He said "this is my body" He was presiding over the meal and giving bread which He said was Himself.
Joachim Jeremias detailed the connection between the Bread of Life Discourse and Paul's instructions from Jesus on the Eucharist:
The fact that in John 6.51c-58 traditional eucharistic material has been used is confirmed by an observation made by J.H. Bernard in 1928. He recognized that we have in John 6.51c an independent version of Jesus' word of interpretation over the bread. One needs only to set John 6.51c and 1 Cor. 11.24b side by side to be convinced of the correctness of this insight:
John 6.51c 1 Cor. 11.24b
the bread which I will give this
is my flesh is my body
for the life of the world which is for you
It can be seen that the structure and content of the sentence is the same in both cases. John has only expanded it paraphrastically at the beginning and at the end.3
For Jeremias, the Bread of Life Discourse is liturgical, having the elements and the homily:
The whole sequence of thought in the discourse on the bread of life now becomes clearer: its conclusion (6.53-58) is a eucharistic homily, the theme of which is introduced by the word of interpretation to the bread (6.51c). John therefore, although he does not mention the institution of the Lord's Supper, introduces the word of interpretation to the bread in the context of a discourse by Jesus, without it thereby (as the history of the research shows) becoming immediately evident as such...the point is that in John 6.51c, 53-58 we meet with a sequence of word of interpretation and its exposition. For here, we may assume, we have an example of the way in which the 'proclamation of the death of the Lord' was carried out at the celebration of the Lord's Supper (1 Cor. 11.26).4
Inefficacy from Unbelief
C.K. Barrett notes what is implied in the actions of Jesus at the Last Supper, is found explicitly stated in the Bread of Life Discourse:
The discourse as a whole is simple, and contains few distinct thoughts; the details on the other hand are often allusive and obscure. It is related both to the synoptic narrative of the feeding of the five thousand (see above, p. 226) and to the eucharistic events of the last supper (Mark 14.22-5; Matt. 26.26-9; Luke 22.14-20), which John does not record. These two meals were probably intended to represent anticipations of the banquet of the kingdom of God, in which the redeemed would enjoy eternal fellowship with their Redeemer. In John's treatment of the theme Jesus takes an even more significant place. Not merely does he miraculously create and distribute the food men need, he is that food, and gives himself, his flesh and blood, for the life of the world. This thought is implicit in the acts of Jesus at the last supper; it becomes explicit in the present discourse.5
Barrett offers a different insight into the overall tenor of the passage which he says shows John assumes and knows his readers will assume the eucharist:
It is perhaps too much to call the discourse a "sacramental" discourse. John is less ready than some of his commentators to argue about the eucharist; he assumes it, and knows that his readers will assume it, while he also knows that except in the context of the fulfillment of God's purpose in the life, death, and resurrection of Jesus it is a meaningless ceremony.6
Barrett sees the emphasis on the importance of belief Jesus fulfilled God's purpose to avoid a meaningless ceremony. This antithetic element would be the fourth division, or the conclusion to the Bread of Life Discourse:
But there are some of you who do not believe.” (For Jesus knew from the beginning who those were who did not believe, and who it was who would betray him.) (John 6:64)
John's account of the Last Supper which lacks the words of institution, includes a unique aspect of the betrayal, which also parallels Paul:
I am not speaking of all of you; I know whom I have chosen. But the Scripture will be fulfilled, ‘He who ate my bread has lifted his heel against me.’ I am telling you this now, before it takes place, that when it does take place you may believe that I am he. (John 13:18-19)
…the Lord Jesus on the night when he was betrayed took bread...Whoever, therefore, eats the bread or drinks the cup of the Lord in an unworthy manner will be guilty concerning the body and blood of the Lord. Let a person examine himself, then, and so eat of the bread and drink of the cup. For anyone who eats and drinks without discerning the body eats and drinks judgment on himself. (1 Corinthians 11:23, 27-29)
"He who ate my bread has lifted his heel against me," had been predicted at the end of the Bread of Life Discourse and highlights the inefficacy of eating without believing. This detail illuminates the opening and closing of Paul's instructions as Judas ate the bread in an unworthy manner not discerning the Lord's body and brought judgment on himself.
John ends the betrayal with, "...believe that I am he." That is, "believe I am He who is gives Himself as the Bread of Life." Catrin H. Williams states of this "I am:"
Jesus, by pronouncing ἐγώ εἰμι, emphasizes that he has been sent as God's representative (cf. v. 3: ὅτι ἀπὸ Θεοῦ ἐξῆλθεν) to make eschatological salvation a reality for believers. This is confirmed by the 'Synoptic' logion included in v. 20 (cf. Matt. 10:40; Luke 10:16), which despite no obvious links with the earlier announcement of betrayal, stresses that the union between Jesus and his disciples is a reflection of his union with the Father (τὸν πέμψαντά με).7
The Passover meal is a family event presided over by the father. At the Last Supper Jesus has assumed the father's position in order to observe the meal with His future family (cf. John 1:12) and to provide Himself as the bread.
1. J. H. Bernard, A Critical and Exegetical Commentary on the Gospel of St. John, Vol 1 p. clxvii
2. Ibid., p clxix
3. Joachim Jeremias, The Eucharistic Words of Jesus, Translated by Norman Perrin, SCM Press Ltd, Trinity Press International, 1966, p. 107-108
4. Ibid., p. 108
5.C.K. Barrett, The Gospel According to St. John, S●P●C●K, 1962, p. 236
7. Catrin H. Williams, I Am He, Mohr Siebeck, 2000, pp. 286-287
8. Barrett, p. 228