Though language referring to Jesus’s death as “for us” and as a “sacrifice” goes back to the New Testament, the substitutionary understanding of this language was first articulated in 1097 by Anselm of Canterbury. His book Cur Deus Homo? addressed the question: Why did God became human, incarnate in Jesus? His answer was that God’s retributive justice requires that the penalty for our sins must be paid from the human side.