Then (or, better, therefore) said Thomas, which is called Didymus. — The second of these names is the Greek translation of the first, which is Hebrew. Both mean “twin.” Both are found together again in John 20:24; John 21:2. Comp. Notes on the Catalogues of the Apostles in Matthew 10:3; Mark 3:18; Luke 6:15, in all of which he is coupled with Matthew, whose twin-brother he possibly was; and in Acts 1:13, where he is coupled with Philip. The name belonged probably to his childhood, and we are wholly without the knowledge which can explain it. The various theories which attempt to do so, from the statement of the Apostolical Constitutions that he had a twin sister Lydia, to the view that the name was given by our Lord to signify his double or halting spiritual nature, are never more than, and are sometimes much less than, elaborate guesses. We may well believe that the name is due to the fact that he was a twin, but of whom it is of no importance that we should know, and it is quite certain that we cannot know.
And yet Peter, John, and Judas, are the only Apostles whose characters we know as well. This is owing to three incidents preserved to us by St. John — the present passage, John 14:5, and John 20:24 et seq. We have before us here a man looking at events from a mind full of the darkest apprehension. He is without hope that a return to Judæa can have any but one issue for his Master. The night is so clearly seen that the brightness of day is obscured. But with all this there is the full love of a devoted disciple, who will follow his Master even unto death.