John Gill

For he knew who should betray him,.... That is, Jesus, as Beza's ancient copy, and the Syriac and Persic versions read. This he knew from the beginning; not only from the beginning of his ministry, when he chose his twelve apostles, but from the beginning of time, yea, from everlasting; this being fixed by the determinate counsel of God, which he, as the omniscient God, was privy to: he knew what preparations were making, and how things were then working, in order to bring it about; he knew that Satan had already put it into Judas's heart, and that he had consented to it; therefore, said he, ye are not all clean: he does not mention his name, though he could have done so, it not being as yet proper to make so full a discovery of him, before the matter was ripe for execution; and also to put all the disciples upon examination of themselves.