In the fateful and controversial passage, John 6:56-57, Jesus Christ exclaims that "he" who feeds on the flesh and blood (ὁ τρώγων μου τὴν σάρκα καὶ πίνων μου τὸ αἷμα) of the Lord remains "in union with" him (NWT).
This account has caused no little dissension among scholars and Bible students as some have taken the verse as an allusion to the Eucharist while others view it as a call to discipleship in general. Vs. 57 seems to help us out here when it goes on to say: "Just as the living Father sent me forth and I live because of the Father, he also that feeds on me, even that one will live because of me" (καθὼς ἀπέστειλέν με ὁ ζῶν πατὴρ κἀγὼ ζῶ διὰ τὸν πατέρα, καὶ ὁ τρώγων με κἀκεῖνος ζήσει δι’ ἐμέ).
So Jesus posits a "just as" (καθὼς) relationship between the believer who feeds on the Son, and the Son who exists because of the "living Father" (ὁ ζῶν πατὴρ). John 6:57 indicates that 6:56 does not have reference to the Eucharist, but instead speaks of the faith that followers of Jesus personally exercise in his ransom sacrifice. Nothing about the context indicates that the Eucharist is the focus:
"These words are at the heart of the discourse on the Bread of Life, and have created great misunderstanding among interpreters. Anyone who is inclined in the least toward a sacramental viewpoint will almost certainly want to take these words as a reference to the sacrament of the Lord's Supper, because of the reference to eating and drinking. The participle in verse 54, τρώγων, is almost shockingly graphic: it means to eat noisily, often used of animals ('gnaw,' 'nibble,' 'munch'). When used with reference to people, it often has the idea of enjoyment (Matt 24:38) and close comradeship. Some have thought it refers to a literal feeding, and thus to the Eucharist. But this does not follow: by anyone's definition there must be a symbolic element to the eating which Jesus speaks of in the discourse, and once this is admitted, it is better to understand it here, as in the previous references in the passage, to a personal receiving of (or appropriation of) Christ and his work" (W. Hall Harris). See https://bible.org/seriespage/9-exegetical-commentary-john-6
Moreover, scholar J.R. Michaels suggests that 6:57 still applies to the Son: He continues to live (even now) by virtue of the Father. This understanding would be in harmony with John 5:26; 14:19. At any rate, John 6:56-57 is not about the Eucharist; its contents pertain to the faith that Christians have in the Messiah (John 6:40).