Although the doors were locked, 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; and put out your hand, and place it in my side. Do not disbelieve, 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 believed." (John 20:26-29 ESV)
On the Second Sunday of Pascha the Church celebrates the confirmation of the resurrection of Christ. Thomas, one of the Twelve, was not with the other disciples when Jesus appeared to them on the evening of that first day of the week. Despite the testimony of others that they had seen the Lord, Thomas challenged the reality of the Resurrection until he could see for himself. Eight days later they had again gathered behind locked doors. Thomas, upon seeing the risen Lord for himself cried "My Lord and my God!" Jesus then said to him: “Have you believed because you have seen me? Blessed are those who have not seen and yet have believed." It is not because of historical evidence or miracles that we are called to believe. We are called to believe because we have accepted the grace of God found in the preaching of the Good News.
For more reading: Paschal Homily of St. John Chrysostom