A.T. Robertson Commentary John 13:21

"When Jesus had thus said, he was troubled in the spirit, and testified, and said, Verily, verily, I say unto you, that one of you shall betray me." — John 13:21 (ASV)

He was troubled in the spirit (εταραχθη το πνευματ). First aorist passive indicative of ταρασσω and the locative case of πνευμα. See already 11:33; 12:27 for this use of ταρασσω for the agitation of Christ's spirit. In 14:1,27 it is used of the disciples. Jesus was one with God (5:19) and yet he had our real humanity (1:14).

Testified (εμαρτυρησεν). First aorist active indicative of μαρτυρεω, definite witness as in 4:44; 18:37.

One of you shall betray me (εις εξ υμων παραδωσε με). Future active of παραδιδωμ, to betray, the word so often used of Judas. This very language occurs in Mr 14:18; Matthew 26:21 and the idea in Lu 22:21. Jesus had said a year ago that "one of you is a devil" (John 6:70), but it made no such stir then. Now it was a bolt from the blue sky as Jesus swept his eyes around and looked at the disciples.