Mathias Gothart Neidhart, known to us as Mathias Grünewald, undoubtedly had a special affinity for Reformation thought. This study presents Grünewald's relationship with Luther's theology of the cross. For the first time, Luther's sermons, which Grünewald deposited in his estate, have been examined in detail for traces in Grünewald's work. The iconography of the crucifixion and the pointing finger of John the Baptist, a theological symbol of justification from the Reformation, holds a prominent position in this context. Ultimately, the aim is not to confessionalize Grünewald. He remained loyal to his church, but he thought and painted in a complementary manner.