"This saying is hard; who can accept it?"
Since Jesus knew that his disciples were murmuring about this,
he said to them, "Does this shock you?
What if you were to see the Son of Man ascending to where he was before?
-- Jn 6:60-69
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
"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."
-- Jn 6:60-69
But Jesus does not give us a formula to repeat mechanically. As in every vocal prayer, it is through the Word of God that the Holy Spirit teaches the children of God to pray to their Father. Jesus not only gives us the words of our filial prayer; at the same time he gives us the Spirit by whom these words become in us "spirit and life." Even more, the proof and possibility of our filial prayer is that the Father "sent the Spirit of his Son into our hearts, crying, 'Abba! Father!'" Since our prayer sets forth our desires before God, it is again the Father, "he who searches the hearts of men," who "knows what is the mind of the Spirit, because the Spirit intercedes for the saints according to the will of God." The prayer to Our Father is inserted into the mysterious mission of the Son and of the Spirit.
-- CCC 2766