“Give me a drink,” Jesus commands the Samaritan woman at the well (John 4:7). There is little human about the Jesus of John’s gospel—or the haloed figure in this early-sixth-century mosaic from the church of Sant’Apollinare Nuovo, in Ravenna, Italy. Jesus asks the Samaritan woman for water, not because he is thirsty, but to teach her a lesson about eternal life. “Everyone who drinks this water,” Jesus tells her, “will be thirsty again; but whoever drinks the water I shall give will never again be thirsty. The water that I shall give will be a spring of water within them, welling up and bringing eternal life” (John 4:13–14).