John 20:25

I will not believe. St. Cyril thinks, that the grief and trouble St. Thomas was under, might partly excuse his want of belief: however, we may take notice with St. Gregory, the his backwardness in believing, was permitted for the good of Christians in general, that thereby they might be more convinced of Christ's resurrection. (Witham) --- The doubts of St. Thomas are of greater advantage to the strengthening of our faith, than the ready belief of the rest of the apostles. For when he proceeded to touch, to assure his faith, our minds, laying aside every, even the least doubt, are firmly established in faith. (St. Gregory the Great)