Jesus did go through the trouble of explaining the parable of the Sower to His disciples. So just because a believer does not understand nor rightly divide the word of truth now, it does not mean they never will.
In the case of eating His flesh and drinking His blood in John 6th chapter, it was never about communion but about believing in His crucifixion how we are saved by believing in Him & His words.
Jesus referred also to His ascension to His disciples before the majority of them had departed in that chapter as if would they believe in Him then.
John 6:60 Many therefore of his disciples, when they had heard this, said, This is an hard saying; who can hear it?
61 When Jesus knew in himself that his disciples murmured at it, he said unto them, Doth this offend you?
62 What and if ye shall see the Son of man ascend up where he was before?
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.
64 But there are some of you that believe not. For Jesus knew from the beginning who they were that believed not, and who should betray him.
Believers that apply His words as if eating my flesh and drinking my blood as referring to communion would be turning the bread & wine into idolatry rather than what God had meant in referring to and indeed what communion is to be referring to also; His crucifixion, thus proclaiming the Lord's death till He comes in remembrance of him only... thus having eyes to see and ears to hear as when His words are used as symbolic rather than literally.
Amen...