Charles Ellicott 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 says He to Thomas...—This implies a knowledge of the words of John 20:25, which in itself would carry conviction to the mind of Thomas. This repetition must have carried with this conviction a sense of shame at his unbelief.

And be not faithless, but believing.—Better, and become not unbelieving, but believing. The words do not apply to the fact of the Resurrection only, but to the general spiritual condition of the Apostle. He was in danger of passing from the state of a believer in Christ to that of an unbeliever. His demand for the evidence of the senses was a step backward, a resting on the less, not on the more, certain. His Master would have him retrace that step, and become one who rests upon the intuition of the Spirit.