+Jn 20: 19-31
On the evening of that first day of the week, when the doors were locked, where the disciples were, for fear of the Jews, Jesus came and stood in their midst and said to them, “Peace be with you.”
When he had said this, he showed them his hands and his side. The disciples rejoiced when they saw the Lord.
(Jesus) said to them again, “Peace be with you. As the Father has sent me, so I send you.”
And when he had said this, he breathed on them and said to them, “Receive the holy Spirit.
Whose sins you forgive are forgiven them, and whose sins you retain are retained.”
Thomas, called Didymus, one of the Twelve, was not with them when Jesus came.
So the other disciples said to 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 into the nailmarks and put my hand into his side, I will not believe.”
Now a week later his disciples were again inside and Thomas was with them. Jesus came, although the doors were locked, and stood in their midst and said, “Peace be with you.”
Then he said to Thomas, “Put your finger here and see my hands, and bring your hand and put it into my side, and do not be unbelieving, but believe.”
Thomas answered and said to him, “My Lord and my God!”
Jesus said to him, “Have you come to believe because you have seen me? Blessed are those who have not seen and have believed.”
Now Jesus did many other signs in the presence of (his) disciples that are not written in this book.
But these are written that you may (come to) believe that Jesus is the Messiah, the Son of God, and that through this belief you may have life in his name.
The New American Bible
The Catechism of the Catholic Church
644 Even when faced with the reality of the risen Jesus the disciples are still doubtful, so impossible did the thing seem: they thought they were seeing a ghost. “In their joy they were still disbelieving and still wondering.” Thomas will also experience the test of doubt and St. Matthew relates that during the risen Lord’s last appearance in Galilee “some doubted.” Therefore the hypothesis that the Resurrection was produced by the apostles’ faith (or credulity) will not hold up. On the contrary their faith in the Resurrection was born, under the action of divine grace, from their direct experience of the reality of the risen Jesus.