Joseph Benson's Commentary of the Old and New Testaments - John 20:24-25
John 20:24-25. But Thomas, called Didymus That is, the twin; was not with them when Jesus came The cause of his absence is not mentioned. Possibly it might be affliction, or some other unavoidable hinderance. Through this, however, he missed the satisfaction and happiness of seeing his Master risen, and of sharing with the disciples in their joy upon that occasion. Here we may observe, those know not what they lose who unnecessarily and carelessly absent themselves from the stated, solemn... read more
Albert Barnes' Notes on the Whole Bible - John 20:25
Except I shall see ... - It is not known what was the ground of the incredulity of Thomas. It is probable, however, that it was, in part, at least, the effect of deep grief, and of that despondency which fills the mind when a long-cherished hope is taken away. In such a case it requires proof of uncommon clearness and strength to overcome the despondency, and to convince us that we may obtain the object of our desires. Thomas has been much blamed by expositors, but he asked only for proof that... read more