Nearly half the people on Earth trace their faith back to Abraham. But “Judaism,” “Christianity” and “Islam” are not single, uniform systems — each is closer to a family of traditions that share a common ancestor and then diverged, sometimes over a word of theology, sometimes over who has the right to lead. Understanding today’s headlines — from debates over women’s ordination to Sunni-Shia tensions to arguments inside Israel over who counts as a Jew — starts with understanding these internal branches.

What follows is a field guide: what each branch believes, how authority works inside it, and the fault lines that still run through each community today.

I.Judaism’s Expanding Branches

From strict Halakhic observance to cultural civilization — six distinct ways of being Jewish.

II.Where the Three Faiths Agree, Diverge and Collide

Five doctrinal fault lines, compared side by side.

III.The Bones of Contention, Summarized

Each faith’s founding schism — and the tension still shaping it today.

None of these divisions are museum pieces. They surface in real disputes over Israeli religious law, in Vatican debates over the diaconate, in Iranian and Saudi rivalry for leadership of the Muslim world, and in every congregation deciding, this week, who is allowed to stand at the pulpit or lead the prayer. Understanding the branch is often the fastest way to understand the headline.