I had been coming to Jerusalem often in recent years. My visits were part of a larger experience of trying to understand the roots of my identity by reentering the landscape of the Bible. I did most of my traveling during a rare bubble of peace, when going from one place to another was relatively easy. Now that bubble had burst, and the world that seemed joined together by the navel was suddenly unraveling around the very same hub: East and West; Arabs and Israelis; Jews, Christians, and Muslims. Words like apocalypse, clash of civilizations, crusade, jihad resounded in the headlines. "We are in a world war," Abdul, the Arab shopkeeper, had said, "a religious war, and it's based just outside my front door."

My experience in the region persuaded me that it's possible – maybe even necessary – to gain insight into a contemporary situation by turning away from the present and looking back to its historical source. Especially in matters of faith, even the most modern act is informed by centuries of intermingled belief, blood, and misunderstanding.

And in that conflagration, as it has for four millennia, one name echoes behind every conversation. One figure stands at the dawn of every subsequent endeavor. One individual holds the breadth of the past – and perhaps the dimensions of the future – in his life story.

Abraham.

The great patriarch of the Hebrew Bible is also the spiritual forefather of the New Testament and the grand holy architect of the Koran. Abraham is the shared ancestor of Judaism, Christianity, and Islam. He is the linchpin of the Arab-Israeli conflict. He is the centerpiece of the battle between the West and Islamic extremists. He is the father – in many cases, the purported biological father – of twelve million Jews, two billion Christians, and one billion Muslims around the world. He is history's first monotheist.

And he is largely unknown.

I wanted to know him. I wanted to understand his legacy – and his appeal. I wanted to discover how he managed to serve as the common origin for his myriad of descendants, even as they were busy shoving one another aside and claiming him as their own. I wanted to figure out whether he was a hopeless fount of war or a possible vessel for reconciliation.

But where could I find him? Abraham, if he existed at all, left no evidence – no buildings or rugs or love letters to his wife. Interviewing people who knew him was out of the question, obviously; yet half the people alive claim to be descended from him. The Hebrew Bible discusses his life, but so do the New Testament and the Koran – and they often disagree, even on basic matters. Going to places he visited, as fruitful as that has been for me and for others, also has its limitations, because Abraham's itinerary changed from generation to generation, and from religion to religion.

I would have to design an unconventional journey. If my previous experience in the region involved a journey through place – three continents, five countries, four war zones – this would be a journey through place and time – three religions, four millennia, one never-ending war. I would read, travel, seek out scholars, talk to religious leaders, visit his natural domain, even go home to mine, because I quickly realized that to understand Abraham I had to understand his heirs.

And there are billions of those. Despite countless revolutions in the history of ideas, Abraham remains a defining figure for half the world's believers. Muslims invoke him daily in their prayers, as do Jews. He appears repeatedly in the Christian liturgy. The most mesmerizing story of Abraham's life – his offering a son to God – plays a pivotal role in the holiest week of the Christian year, at Easter. The story is recited at the start of the holiest fortnight in Judaism, on Rosh Hashana. The episode inspires the holiest day in Islam, 'Id Al-Adha, the Feast of the Sacrifice, at the climax of the Pilgrimage.

And yet the religions can't even agree on which son he tried to kill.

What they do concur in is that Abraham occupies such sacred space because he is the first person to understand that there is only one God. This is his greatest contribution to civilization and the shared endowment of the Abrahamic faiths. It gives him power, but is also a flash point, as everyone wants dominion over that moment. Muhammad may be more important for Muslims, Jesus for Christians, and Moses for Jews; yet all three traditions go out of their way to link themselves to their common patriarch. It's as if Abraham were the Rock, tugging everyone to a common hearth, the highest place, the earliest place. The place closest to God. Control the Rock and you control Abraham. Control Abraham and you control the threshold to the divine.

And so I returned to Jerusalem. I came alone – as everyone does, in a sense – to an uncertain destination. I came because this is the best place to understand Abraham, and to understand what he revealed about God.

And because this is the best place to understand myself.