1st, they came looking for signs (vs. 25-26), then Jesus said to them Laber not what can perish (vs 27), how do they do that? Believe... in Him (vs 29).
2nd, It is then He began to liken Himself to a better bread, and encourage them to believe in Him. Do you see that? He did so all the way to vs 63.
He is telling them intermittently that He... is the bread of life; His body and blood has an eternal value (vs' 48-51).
But the Jews around them took that literallty did they not? They grumbled, saying how can this man tell us to eat him? Finally, in 63, He told them plainly:
63 It is the spirit that quickeneth; the flesh profiteth nothing: the words that I speak unto you, they are spirit, and they are life.
The WORDS He is speaking to them... they are spirit and life.
He had been telling them to BELIEVE IN HIM from the VERY BEGINNING to the VERY END (vs 29, 37-39, 44, 47, ).
So... why would Jesus, in the middle of telling them to believe, introduce the ordinance of the Communion?
The only way you can be justified in believing that is when you ISOLATE passages like vs' 48-51, FROM ITS CONTEXT. By doing that, you can be justified in believing it.
That is wrong.
Just as wrong as taking your words out of context.
That, is one of the main ways of creating false doctrine; and the other way, is to read-in to passages, making it look like something that is not. As an example, the LDS used John 10:16 as an introduction to the Book of Mormon (as according to them, Jesus went to pre-colonial North America to reach out to "the other sheep" while the Other Sheep in the Bible are the Gentiles (Deuteronomy 32:21, Isaiah 42:6, Romans 1:17, & 10:19)
So again, why would Jesus introduce an ordinance, in the middle of what He had been telling them all along?
This is the reason why I don't believe in the literal interpretation of the verses used; the context of the passage is the reason why.