What if you were to see the Son of Man ascending to where he was before?
It is the Spirit that gives life, while the flesh is of no avail.
The words I have spoken to you are Spirit and life.
But there are some of you who do not believe."
The first announcement of the Eucharist divided the disciples, just as the announcement of the Passion scandalized them: "This is a hard saying; who can listen to it?" The Eucharist and the Cross are stumbling blocks. It is the same mystery and it never ceases to be an occasion of division. "Will you also go away?": the Lord's question echoes through the ages, as a loving invitation to discover that only he has "the words of eternal life" and that to receive in faith the gift of his Eucharist is to receive the Lord himself.
-- CCC 1336