The summary will come later.
While reading this, I was thinking of Geert Mak's identity. Maybe I'm seeing too much through the lenses of American tribalism, but I believe I have it figured out.
He's Reformed. Although he might rarely set foot in a Dutch Reformed Church, I think that informs who he is to a great extent. The Reformed are his people. He writes about his family and friends with great affection. The Reformed world and its increasingly byzantine politics was too small, too narrow minded at times, even ridiculous, but it was and remains his own.
Looking back on the book, it's clearer now. Each time the Dutch Reformed Church split, part of the Mak family identity went with it. I think at the core, there is a Reformed identity that supersedes the past century and longs for the unity that Abraham Kuyper preserved.