john 6:53

[prismaticbleed]

"So Jesus said again, “I tell you the truth, unless you eat the flesh of the Son of Man and drink His blood, you cannot have eternal life within you." (John 6:53 NLT)

Note the "CANNOT," not just "do not."
All mortal life is replenished by food, and ALL food is the giving of one lifeform's existence or essence to strengthen another's. Light feeds plants, plants feed animals, animals feed humans. Everything is a sacrificial give-and-take. But note this-- IT IS ALL MORTAL. We don't just eat once and that's it forever. No, we also DIE daily, in apoptosis and disease and age. We constantly need new food-- new life-- to continue to exist in these slowly fading bodies. 
This is where Christ steps in.
He is the TRUE Food-- the Bread Of Life. He alone is IMMORTAL, possessing eternal life, untouched by death and forever incorruptible. And what more perfect fulfillment of that maternal instinct, that Self-sacrifice for one's beloved babe, than for Him to play the Pelican and feed us hungry children with His very Blood & Body?
To feed on Him IS to be a helpless infant in His arms. To eat His Flesh & Blood is to accept God's Passover Lamb to save us from doom's swift angel.
What Christ is telling us is true in the most simply profound way: just like no mortal sacrifice could take away sin, so too can no mortal food strengthen our souls. We need something greater, something purer, something real. We need Life and Love. We need HIM. And He GIVES Himself, He Who cannot ever be depleted, both as sacrifice and sustenance, so that we may have His Life-- TRUE Life-- both within and without us, and so be ultimately free of BOTH spiritual & physical death.