60 On hearing it, many of his disciples said, "This is a hard teaching. Who can accept it?"
61 Aware that his disciples were grumbling about this, Jesus said to them, "Does this offend you? 62 What if you see the Son of Man ascend to where he was before! 63 The Spirit gives life; the flesh counts for nothing. The words I have spoken to you are spirit and they are life. 64 Yet there are some of you who do not believe." For Jesus had known from the beginning which of them did not believe and who would betray him. 65 He went on to say, "This is why I told you that no one can come to me unless the Father has enabled him."
A big distinction between Catholic and non-Catholic Christians is the understanding of Jesus' words here. Catholic believe He literally was saying that a wafer could be turned into His flesh for thousands of years after He walked the Earth. The Christian understanding takes into account here that Jesus explains that His words speak of His Spirit. "The flesh profits nothing. The words I have spoken are spirit and they are life."
I often ask Catholics which of these two options would actually bring someone closer to God. First, place a Eucharistic wafer in someone's cereal unbeknownst to them each day for a year? Or, read to that person out of the Bible each day for a year. Which one is actually consuming the Word, Jesus? Which one will actually bring someone to an understanding of the gospel, so they can choose to repent and place their faith in the Savior? It really isn't that complicated.
66 From this time many of his disciples turned back and no longer followed him.
67 "You do not want to leave too, do you?" Jesus asked the Twelve.
68 Simon Peter answered him, "Lord, to whom shall we go? You have the words of eternal life. 69 We believe and know that you are the Holy One of God."
70 Then Jesus replied, "Have I not chosen you, the Twelve? Yet one of you is a devil!" 71(He meant Judas, the son of Simon Iscariot, who, though one of the Twelve, was later to betray him.)