Citation: John 20:24-29 Why this encounter matters: Contains the most explicit confession of Jesus's deity by any single individual in the NT, "My Lord and my God."
The narrative
Thomas (called Didymus, Greek for "twin") was absent at Jesus's first post-resurrection appearance to the disciples (John 20:19-23). The other disciples report: "We have seen the Lord!" Thomas responds:
"Unless I see in his hands the print of the nails, put my finger into the print of the nails, and put my hand into his side, I will not believe."
Eight days later, the disciples are again gathered, Thomas with them. Doors shut. Jesus stands in the midst: "Peace be to you." To Thomas: "Reach here your finger, and see my hands. Reach here your hand, and put it into my side. Don't be unbelieving, but believing."
Thomas: "My Lord and my God!"
Jesus: "Because you have seen me, you have believed. Blessed are those who have not seen, and have believed."
Theological significance
Highest Christological confession in the gospels, "My Lord and my God" (ὁ κύριός μου καὶ ὁ θεός μου ho kurios mou kai ho theos mou) is the most explicit single individual's confession of Jesus's divinity in the gospels. John 20:30-31 follows immediately: "these are written, that you may believe that Jesus is the Christ, the Son of God; and that believing you may have life in his name", Thomas's confession is the gospel's climactic substance.
Did Jesus accept the title? Yes. Jesus does not correct Thomas's "Lord and God", affirming the appropriateness of the address. Compare with Revelation 19:10 + Revelation 22:9 where an angel refuses worship ("You must not do that!"). Jesus accepts what an angel rejects.
Doubt-to-faith pattern, Thomas's question is honest doubt, not faithlessness. He wants the same evidence the others had (John 20:20, Jesus showed them hands + side). The encounter validates: tactile evidence offered, doubt resolved, faith deepened.
Blessing on later believers, Jesus's "Blessed are those who have not seen and have believed" extends the encounter forward to every Christian after the apostolic generation. Anti-blessing on first-generation seeing-then-believing? No, Jesus blesses Thomas's faith too. Rather: blessing extends specifically to the post-apostolic non-seeing church.
"Doubting Thomas" tradition
"Doubting Thomas" has become a proverb for any skeptic. The text is more nuanced, Thomas's "doubt" is the demand for empirical confirmation, which Jesus offers + accepts. Thomas's later traditional ministry, apostle to India per early-church tradition (the Mar Thoma Christians of Kerala trace founding to him), shows that his doubt-resolved becomes lifelong commitment.