Expositor's Bible Commentary Commentary John 12:36

"While ye have the light, believe on the light, that ye may become sons of light. These things spake Jesus, and he departed and hid himself from them." — John 12:36 (ASV)

Jesus spoke with urgency. The light would not always be available (cf. 9:4). If his hearers wished to walk with certainty, they should act at once, for after his departure they might find themselves in the darkness. “Put your trust” implies a persistent faith, not solely a momentary decision (cf. 14:1).