The Incredulity of Saint Thomas is one of the most copied and reproduced of all Caravaggio paintings. According to the gospel of St. John, Thomas (one of the twelve apostles) had missed Christ's appearance after the Resurrection and insisted that "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 it." One week later, Christ appeared to Thomas instructing him: ”Reach hither thy hand, and thrust it into my side: and be not faithless, but believing.” Thomas was thus convinced (about the Resurrection) and proclaimed: “My Lord and my God!”, to which Jesus responded, “Because you have seen me, you have believed; blessed are those who have not seen and yet have believed.” 

this work is oil on canvas  and is in the  Sanssouci, Potsdam, Berlin, Germany

In Caravaggio’s composition, light streams into the image from the left side of the frame, bathing Jesus in a warm glow. He and the apostles are tightly arranged, with Jesus and Thomas occupying the forefront. Caravaggio's painstaking attention to veristic (a realistic style in Roman portraiture) detail is most evident in the torn seam on the left shoulder of Thomas's shirt, on the marks on Jesus's torso, and in Thomas's dirty fingernails. Moreover, while The Incredulity of Saint Thomas was a popular subject in Renaissance and Baroque art, Caravaggio's gruesome focus on Thomas's finger probing Christ's gaping wound distinguished the work from all others on the same theme. 

Such a painting might have struck devout people as irreverent and even outrageous. They were accustomed to seeing the apostles as dignified figures draped in beautiful folds, and here they looked like common laborers, with weathered faces and wrinkled brows. But, Caravaggio would have answered, they were old laborers, common people. 

Many art historians have said Caravaggio’s painting placed him in the company of such greats as Giotto and Dürer before him since, like them, he had wanted to see the holy events before his own eyes as if they were happening in a neighbor’s house.