My first real experience of the patriarch Abraham’s crossover appeal came on the splendid sun-spangled day in June when I took a crosstown cab to arrange my son’s circumcision. Jews have circumcised for thousands of years–ever since God , having made a history-altering pact with Abraham, directed him to “cut my Covenant in your flesh.” Some biblical commentators suggest that the circumcision was meant as much as a reminder to the Lord as to the Israelites, a kind of divine Post-it not to extirpate these people. My thought as we rolled eastward across Manhattan was, There must be easier ways. We slowed behind traffic on one of the roads through Central Park, and I found myself tapping my foot. The tune on the cab’s stereo was Arabic but with a catchy, bubbling horn section. I asked who was playing. A Moroccan group, said the cabbie. He told me its name. Did I want to know what it was singing? Certainly. It was a plea to Israel from the Arab people. The chorus was, “We have the same father. Why do you treat us this way?” Who might the father be? I asked. “Ibrahim,” he said. “The song is called Ismail and Isaac,” after his sons. We have the same father. Why do you treat us this way? What did that scrap of a song hint at? First of all, it gave witness that a figure beloved by Jews and Christians has a Muslim constituency, suggesting a connection between Islam and the West that might surprise most Americans in this tense season. But second, it acknowledged that despite this apparent bond, there is still turmoil among the sons of Abraham. It wouldn’t do to call Abraham a neglected giant of the Bible; almost everyone knows the outline of his story. But until recently he probably has not received the credit he deserves as a religious innovator. Asbiblical pioneer of the idea that there is only one God, he is on a par with Moses, St. Paul and Muhammad, responsible for what Thomas Cahill, author of the 1998 history The Gifts of the Jews, calls “a complete departure from everything that has gone before in the evolution of culture and sensibility.” In other words, Abraham changed the world. Even less well known to most Americans is the breadth of his following. Jews, who consider him their own, are largely unaware of Abraham’s presence in Christianity, which accepts his Torah story as part of the Old Testament and honors him in contexts ranging from the Roman Catholic Mass to a Protestant children’s song .