60 Therefore many of his disciples, when they heard this, said, “This is a hard saying! Who can listen to it?”

61 But Jesus knowing in himself that his disciples murmured at this, said to them, “Does this cause you to stumble? 62 Then what if you would see the Son of Man ascending to where he was before? 63 It is the spirit who gives life. The flesh profits nothing. The words that I speak to you are spirit, and are life. 64 But there are some of you who don’t believe.” For Jesus knew from the beginning who they were who didn’t believe, and who it was who would betray him. 65 He said, “For this cause have I said to you that no one can come to me, unless it is given to him by my Father.”

66 At this, many of his disciples went back, and walked no more with him. 67 Jesus said therefore to the twelve, “You don’t also want to go away, do you?”

68 Simon Peter answered him, “Lord, to whom would we go? You have the words of eternal life. 69 We have come to believe and know that you are the Christ, the Son of the living God.”

John 6:60-69 - World English Bible

After the Eucharistic pronouncement in John 6, many of Jesus' disciples turned away. They were attracted by his signs and his teaching, but could not abide the command to "eat his flesh and drink his blood" (6:53-56). Consuming blood and cannibalism were abhorrent to Judaism, and these former followers could not go on, even as the Lord reminded them of his origin (6:62). Their earthly thinking ("flesh") could not comprehend revelation ("words of spirit and life"). No wonder, for faith is a gift from the Father (6:65).

What would happen to those who remained? Would they leave? Peter had it completely right:

“Lord, to whom would we go? You have the words of eternal life. We have come to believe and know that you are the Christ, the Son of the living God.” (6:68-69)

Why do you remain a Christian?