A.T. Robertson Commentary John 20:27

"Then saith he to Thomas, Reach hither thy finger, and see my hands; and reach [hither] thy hand, and put it into my side: and be not faithless, but believing." — John 20:27 (ASV)

Then saith he to Thomas (ειτα λεγε τω Θομα). Jesus turns directly to Thomas as if he had come expressly for his sake. He reveals his knowledge of the doubt in the mind of Thomas and mentions the very tests that he had named (25).

Be not faithless (μη γινου απιστος). Present middle imperative of γινομα in prohibition, "stop becoming disbelieving." The doubt of Thomas in the face of the witness of the others was not a proof of his superior intelligence. Sceptics usually pose as persons of unusual mentality. The medium who won Sir Arthur Conan Doyle to spiritualism has confessed that it was all humbug, but he deceived the gullible novelist. But Thomas had carried his incredulity too far. Note play on απιστος (disbelieving) and πιστος (believing).