But there are some of you that believe not.
For Jesus knew from the beginning who they were that believed not, and who would betray him.
All Commentaries on John 6:64 Go To John 6
John Chrysostom
AD 407
Again, according to His custom, He adds weight to His words, by foretelling what would come to pass, and by showing that He spoke thus not from desire of honor from them, but because He cared for them. And when He said some, He excepted the disciples. For at first He said, You have both seen Me, and believe not John 6:36; but here, There are some of you that believe not.
For He knew from the beginning who they were that believed not, and who should betray Him.