When it was evening on that day, the first day of the week, and the doors of the house where the disciples had met were locked for fear of the Jews, Jesus came and stood among them and said, 'Peace be with you.' After he said this, he showed them his hands and his side. Then the disciiples rejoiced when they saw the Lord.....
But Thomas (who was called the Twin), one of the twelve, was not with them when Jesus came. So the other disciples told him, 'We have seen the Lord.' But he said to them, 'Unless I see the mark of the nails in his hands, and put my finger in the mark of the nails and my hand in his side, I will not believe.'
A week later his disciples were again in the house, and Thomas was with them. Although the doors were shut, Jesus came and stood among them and said, 'Peace be with you.' Then he said to Thomas, 'Put your finger here and see my hands. Reach out your hand and put it in my side. Do not doubt, but believe.' Thomas answered him, 'My Lord and my God!' Jesus said to him, 'Have you believed because you have seen me? Blessed are those who have not seen and yet have come to believe.'
(Church in Wales Lectionary, New Revised Standard Version)
We all make mistakes, but often expect others to be perfect, and can judge them by one mistake. We remember Jacob stole his brother's birthright, forgetting all that he went on to do; and that Peter denied knowing Jesus, but went on to create the new Church. As for Thomas, we remember him because of his doubt, yet tradition says he took Christianity to India.
Thomas was a practical realist who wanted to be sure. He was no different to the other disciples. Luke's Gospel and Mark's (in his extended version) both record that the disciples refused to believe Mary when she tells them Jesus has risen.
But there is a difference between an honest and a dishonest doubter. Some people prefer their ungodly life, and don't want to believe. This was not Thomas, and Jesus knew that once Thomas found a way forward through his doubts, he would be the staunchest of Christians. If you have doubts, ask God to help remove them.
Heavenly Father,
You know the inner secrets
of our hearts -
the way we sometimes
pretend confidence in our faith,
and act as though all is well.
Give us a sure knowledge,
and a firm foundation for faith,
and keep us ever asking for Your help.
Amen.
The Britannica Encyclopedia has some more information on Thomas, but it's what we might call "tradition", and there are only a few facts: