The numbering of the verse you cite is coincidental with the Revelation “Beast” prophecy; after all, the Canon of Scripture was not divided into the chapters and verses we know today until AD 1548. That being said, the theology behind your assertion is quite sound: those who knowingly refuse to eat the Flesh and drink the Blood of Jesus Christ are lost.
May God have mercy on all of us poor sinners.
I do realize the numbers in the Gospel of John, 6:66, were added later, and are not in the original manuscript. But if John’s Revelation really is a prediction — a vision of what the future holds, as many take Revelation to be — then that future would include the eventual association of the Number of the Beast, 666, with the Gospel of John, Chapter 6, Verse 66. At least this interpretation makes more sense than accusing every new world leader of being the anti-Christ and finding some way to link the claim to Scripture, which seems to be a tradition...
That’s nonsense. You are lost when you don’t accept Him into your life and walk with Him. Eating a wafer won’t do it. The wafer has no magical significance in salvation. Your CHOICE to receive Christ as Saviour does.