Do you know the story behind this commonly used phrase?
Jesus came back after rising from the grave to visit his disciples, and they were excited of course, and Thomas was not with them. When Thomas had returned again to the house where they were meeting, they told Thomas of the Lord visiting them. Even though there were ten witnesses that walked with Jesus while he was alive, giving their testimony to Thomas, he said he would not believe, until he saw the scars in his palms, and the hole in his side, where Christ was speared.
When Jesus returned a few days later, he made his presence known and called Thomas to see the scars and to thrust his hand inside the hole in his side.
Here is the passage in the NIV...
24 Now Thomas (also known as Didymus[a]), one of the Twelve, was not with the disciples when Jesus came. 25 So the other disciples told him, “We have seen the Lord!” But he said to them, “Unless I see the nail marks in his hands and put my finger where the nails were, and put my hand into his side, I will not believe.”
26 A week later his disciples were in the house again, and Thomas was with them. Though the doors were locked, Jesus came and stood among them and said, “Peace be with you!” 27 Then he said to Thomas, “Put your finger here; see my hands. Reach out your hand and put it into my side. Stop doubting and believe.”
28 Thomas said to him, “My Lord and my God!”
29 Then Jesus told him, “Because you have seen me, you have believed; blessed are those who have not seen and yet have believed.”
GOD works in our lives today. Believe, and you will be saved. So please, never be a "doubting Thomas".