John 6:62-64

What then [will you think] if you see the Son of Man ascending to [the realm] where He was before? It is the Spirit who gives life; the flesh conveys no benefit [it is of no account]. The words I have spoken to you are spirit and life [providing eternal life]. But [still] there are some of you who do not believe and have faith.” For Jesus knew from the beginning who did not believe, and who would betray Him.