When John the Baptist was standing on the bank of the Jordan preaching, he saw Jesus and proclaimed: “Behold the Lamb of God, which taketh away the sin of the world” (John 1:29). After this, the first disciples turned to Jesus. The unknown donor is also instructed by John to follow Christ. This notion is central to the Devotio moderna, a religious movement that spread throughout Europe in the fifteenth century. The subtlety and quality of the painting characterise this work as one of the artist’s undisputed masterpieces.