John 6:63 It is the Spirit who gives life; the flesh is no help at all. The words that I have spoken to you are spirit and life.
Jesus says the Spirit gives life, the flesh is NO HELP AT ALL.
So, which one is correct?
Or did Jesus contradict Himself?
As I'm sure you know, "flesh" is used in several different senses in Scripture. The Gospel of John (ch. 1) begins with "the Word was made Flesh, and dwelt amongst us." Jesus explains in John 6 that the bread which He offers "is My Flesh for the life of the world."
Jesus' Flesh is Sacred because of what the Incarnation actually is: the Second Person of the Trinity, the Word, taking on a true human nature for our sake. Everything about Him is sacred: His sacred Heart, His sacred Head, His sacred Body, His sacred Blood. His sacred humanity.
This avails EVERYTHING.
"Flesh" in another, quite distinct sense means mere fallen humanity, weakened as it is by sin, and not suffused with the power of the Divine. "Flesh" in this usage means not only the carnal body, but also the carnal mind: frail, unenlightened, an intellect stultified by a merely materialist outlook.
"The Spirit is willing, but the flesh is weak."
Christ is not talking about HIS flesh availing nothing. If that were true, then the Incarnation would be pointless. The whole of John 6 would be a meaningless meander ("I'm giving you my flesh which avails nothing?" "Eat this flesh because it avails nothing?)" His Passion, Suffering, and Death would be pointless. His Resurrection, even, would be not a miracle, but a monstrosity: the resuscitation of a corpse. Zombie-Christ.
But that whole line of thought is idiocy. Our salvation is real because the real Christ--- Body, Blood, Soul and Divinity --- has accomplished it. He, Himself: God in the Flesh.