(RNS) — I have done my share of traveling in Europe, and when I am there, I visit cathedrals. Most are majestic, and they are filled with Christian art that would take a decent docent a decade to unpack for me. I have never been to Brussels, though I would like to visit. And when I am there, I expect to make a special trip to the Cathedral of St. Michael and St. Gudula. That is the subject of Flora Cassen’s new book, “Stained Glass: A Reflective History of Antisemitism.” The cathedral is, by all accounts, a masterpiece. Built between the 13th and 15th centuries, it rises above the old town on its own little hill, and when the lights hit the stonework at night, it looks like lace carved out of sky. “Stained Glass: A Reflective History of Antisemitism” by Flora Cassen. (Courtesy image) But I imagine myself stepping inside. I would look intensely and intentionally at the stained-glass windows — the ones donated by Belgium’s first two kings in the 19th century. And …