This verse is part of the discourse not in conclusion or even after the verses I mention. Jesus didn’t changed the subject he was still making his point. Obviously, Catholics believe you may obtain eternal life without ever receiving the Eucharist. How do they then view this verse if not with in a part of the overall discourse about Jesus being from the Father. Manna is bread but not bread of eternal life. Jesus is eternal this eternal bread because he comes from the Father and is part of the Trinity. This part of the discourse contrast Jesus with Manna to which Jesus is showing that he indeed comes from the Father.
I recall having this EXACT same “discussion” on CARM (Christian Apologetics Research Ministry), which is Calvinistic in doctrine, and the CARM scholar frequently referencing D.A. Carson that ALL of St. John 6 is answered in verses 30-35, i.e., supporting the “figurative” speech; unfortunately, if we take the literal meaning of eating flesh and drinking blood" was the idiomatic phrase synonymous with persecution, violence, betrayal, and murder.
A good source is “The Fundamentals of Catholic Dogma” by Dr. Ludwig Ott. Ott states that the body and blood as described by Christ in John 6 (and the synoptic Gospels, too) are not figurative because nowhere else in the Bible (either OT or NT) are the words “body” and “blood” used figuratively. To assign these words “figurative” status, given their specific time 2,000 years ago, means that to the Jews of Christ’s day to “eat someone’s flesh and drink someone’s blood” was synonymous with persecution, violence, betrayal, bitterly hate, and murder. Also, “to drink some one’s blood”, in Scripture, especially, has no other figurative meaning than that of dire chastisement. Examples cited by Ott are:
Micah 3:1-3 You that hate good, and love evil: that violently pluck off their skins from them and their flesh from their bones? 3 Who have eaten the flesh of my people, and have flayed their skin off them: and have broken, and chopped their bones as for the kettle, and as flesh in the midst of the pot.
Isaiah 9:20 20 And he shall turn to the right hand, and shall be hungry: and shall eat on the left hand, and shall not be filled: every one shall eat the flesh of his own arm: Manasses Ephraim, and Ephraim Manasses, and they together shall be against Juda.
Isaiah 49:26 26 And I will feed thy enemies with their own flesh: and they shall be made drunk with their own blood, as with new wine: and all flesh shall know, that I am the Lord that save thee, and thy Redeemer the Mighty One of Jacob.
That’s why, if Jesus had been speaking figuratively, his words would have made no sense at all. He would have been saying, “I solemnly assure you that unless you persecute and betray me you have no life within you. He who does violence to me has eternal life and I will raise him up on the last day.” That makes no sense at all, but that’s exactly what he would have been saying if his words were symbolic.