John 6:62-66

What and if ye shall see the Son of man ascend up where he was before?

It is the spirit that quickeneth; the flesh profiteth nothing: the words that I speak unto you, they are spirit, and they are life.

But there are some of you that believe not. For Jesus knew from the beginning who they were that believed not, and who should betray him.

And he said, Therefore said I unto you, that no man can come unto me, except it were given unto him of my Father.

From that time many of his disciples went back, and walked no more with him.