John 6:64

But there are some of you that believe not,.... Notwithstanding the ministry they sat under, and the words they heard; for though they professed to believe in Jesus, as the Messiah, yet they did not truly believe in him; their faith was not a living faith, or of a spiritual kind, but a mere historical and temporary one, and was feigned and hypocritical:

for Jesus knew from the beginning; of his ministry, and of their profession of him, being God omniscient, and the searcher of hearts:

who they were that believed not; i.e. in him, as the Arabic version reads: notwithstanding their following him, and professing to believe in him, and the great outward respect and esteem they showed to him, he could see through all those masks they put on, and knew they had no true faith of him in them; and the same knowledge he has of every professor of his name: he knows whether their faith is of the right kind or not; whether they have obtained the like precious faith with God's elect; or whether their profession is only a verbal one. In some copies it is read, "who they were that believed"; who were true believers, as well as who were hypocrites.

And who should betray him: he not only knew how it was with the multitude of the disciples that professed love to him, and faith in him; but he also particularly knew the case of the twelve apostles, and that one of them should betray him, and who he was. This was determined in the decrees of God, and was foretold in the prophecies of the Old Testament, and was predicted by Christ; and the person was pointed at by him before it was done.