Now Thomas, one of the twelve, called the Twin, 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 in his hands the mark of the nails, and place my finger into the mark of the nails, and place my hand into his side, I will never believe.”
 Eight days later, his disciples were inside again, and Thomas was with them. 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!”
– John 20:24-28
Even after many of the disciples have seen the risen Jesus, they are hiding. They are afraid to be arrested and killed the way Jesus was. Jesus appears and says, “Peace be with you.”
Then he singles out Thomas. Is Jesus yelling at Thomas for his lack of faith? Is He shaming him by repeating his request? I doubt it. Nearly all the other disciples did not believe before they saw the resurrected Christ either.
Jesus is reaching out to his disciple who has been crushed, who is on the brink of despair. He tells him, “Thomas I hear you. I know you. Your faith wavers, but I am the Good Shepherd, and I leave none of my sheep behind. My grace is for you.”
Next, Jesus tells Thomas, “Do not disbelieve but believe.” Jesus is not asking for general belief. This is not about whether Thomas believes that God exists or that He created the world. Plenty of people believe that. This is not about belief in self or even the strength of one’s faith. Jesus knows Thomas’s faith is not strong enough. Jesus wants Thomas to believe that He is the Son of God and that he can have eternal life in His name.
Faith is not general. It is specific and personal. The Heidelberg Catechism defines faith as follows:
True faith is a sure knowledge whereby I accept as true all that God has revealed to us in His Word. At the same time it is a firm confidence that not only to others, but also to me, God has granted forgiveness of sins, everlasting righteousness, and salvation, out of mere grace, only for the sake of Christ’s merits. This faith the Holy Spirit works in my heart by the gospel.
Do you know that the grace of God is for you? You who are sinful and weak, you who go astray – Jesus died and rose for you! The peace of God is for you!