John 6:60-64

Therefore many of His disciples, when they heard this said, “This is a difficult statement; who can listen to it?” But Jesus, conscious that His disciples grumbled at this, said to them, “Does this cause you to stumble? What then if you see the Son of Man ascending to where He was before? It is the Spirit who gives life; the flesh profits nothing; the words that I have spoken to you are spirit and are life. But there are some of you who do not believe.” For Jesus knew from the beginning who they were who did not believe, and who it was that would betray Him.