Commentaries:
Robertson's Word Pictures (NT)
He was troubled in the spirit (etaraxqh toi pneumati). First aorist passive indicative of tarassw and the locative case of pneuma. See already John 11:33; John 12:27 for this use of tarassw for the agitation of Christ's spirit. In John 14:1, John 14:27 it is used of the disciples. Jesus was one with God (John 5:19) and yet he had our real humanity (John 1:14).
Testified (emarturhsen). First aorist active indicative of marturew, definite witness as in John 4:44; John 18:37.
One of you shall betray me (eiv ec umwn paradwsei me). Future active of paradidwmi, to betray, the word so often used of Judas. This very language occurs in Mark 14:18; Matthew 26:21 and the idea in Luke 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.
Other Robertson's Word Pictures (NT) entries containing John 13:21:
Matthew 6:25
John 4:6
John 12:27
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