In this dramatic test of faith from the Old Testament book of Genesis, Abraham agrees to slay his son Isaac on God’s command. As Abraham raises the knife, an angel suddenly appears to halt the sacrifice. This work gains its power from the complex expressions of father and son, combining grief, strength, resignation, fear, and realization in their faces and bodies, the latter inspired by ancient sculpture and Michelangelo. Andrea del Sarto never finished this painting, and it lays bare his working methods. He transferred the design to the panel from a drawing, reinforcing the chalk with painted lines—best seen in the donkey at the far right. He then worked over the whole panel at once with thin, brushy veils of color, letting him alter the composition while painting—especially evident in the angel, Isaac’s body, and Abraham’s head.