In John 20, Jesus has resurrected from the dead and appeared to many of the disciples who knew him before his crucifixion. They are astonished at what they’re seeing, but they nonetheless believe. One of the disciples, Thomas, hasn’t seen the risen Jesus for himself, but he has been told about him from his fellow disciples.
“We have seen the Lord!” But he said to them, “Unless I see in His hands the imprint of the nails, and put my finger into the place of the nails, and put my hand into His side, I will not believe.” (Jn. 20:24-25, NASB)
You can see the difference between Thomas and the rest of the disciples. Theyhave seen the risen Jesus and, thus, believe. Thomas has not seen and, thus, does not believe.
Mercifully for Thomas—and us—the story does not end there.
John tells us that after some days had passed the disciples were all together again in a room behind a locked door and then Jesus was in there with them. He invites Thomas to see for himself and then instructs him to stop doubting and believe. It’s a wonderfully simple phrase in the Greek New Testament that reads: μὴ γίνου ἄπιστος ἀλλὰ πιστός.
Do not be ἄπιστος (unbelieving), but πιστός (believing).
Next, comes Thomas’s declaration of faith. First the Greek: ἀπεκρίθη Θωμᾶς καὶ εἶπεν αὐτῷ· Ὁ κύριός μου καὶ ὁ θεός μου. In English, the text reads: Thomas answered and said to him: “My Lord and my God.”
Note just two quick things here. 1) The text says that Thomas did two things to one person: he answered and said to αὐτῷ–or him—(i.e., Jesus). There is no hint of Thomas responding and speaking to Jesus and then—somehow in the middle of that—looking up and speaking to the Father. 2) In this statement all directed to Jesus, Thomas calls him both his Lord and his God. It’s clear, that Jesus is Lord (κύριός). Along with that, it’s just as clear that Jesus is God (θεός).