Commenting on John 6, Leonhard Goppelt wrote:
In 6:51, 52 the presentation of the gift unmistakably adopts eucharistic language (in structure and content 6:51c corresponds to the bread saying in 1 C. 11:24b. The terms σαρξ and αιμα, which occur together in Jn. 6:53, are the traditional designation of the eucharistic gift in Ign.) and the eating is characterised as really corporeal by αληθως (-ης). If the intervening v. 54 breaks the many preceding references to εφαγον by using an expression with τρωγω which is repeated three times, this may underline at least the allusion to the eucharist.
This way of introducing the eucharist by the mode of expression is theologically significant. In Jn. 6:51c-58 we do not have the fig. description of one of the Church’s institutions but a direct continuation of the preceding revelatory address. In its mode of expression the section is proclamation which summons to faith, but the formulation shows that this can be truly accepted only in the form of the eucharist. The self-proffering of Jesus by the word becomes the more concrete self-proffering by the eucharist and appropriation by believing hearing becomes correspondingly appropriation by believing eating. The necessity of the eucharist to salvation, which in some sense is stated by Jn. 6:53 as is that of baptism by Jn. 3:5, is thus the necessity of the uncurtailed incarnation of the Word. The connecting line which we discover between Jn. 6:51c-58 and the address on the bread of life is thus an indisputable sign that they belong together. Elimination of this section would destroy the finest presentation of the relation between word and sacrament in the NT (we can put baptism and eucharist together under the later term sacrament because they are associated in Jn 3:5; 6:53; 19:34; 1 Jn. 5:8 as already in 1 C. 10:1-4—so long as we understand by the term what is common to them). (Goppelt, "τρωγω." TDNT 8:236-37, here, p. 237)
