It is also a very curious thing. Why should a 17th-century Portuguese-Jewish philosopher whose dense and opaque writings are notoriously difficult to understand incite such passionate devotion, even obsession, among a lay audience in the 21st century? Part of the answer is the drama and mystery at the centre of his life: why exactly was Spinoza so harshly punished by the community that raised and nurtured him? Just as significant, I suspect, is that everyone loves an iconoclast – especially a radical and fearless one that suffered persecution in his lifetime for ideas and values that are still so important to us today. Spinoza is a model of intellectual courage. Like a prophet, he took on the powers-that-be with an unflinching honesty that revealed ugly truths about his fellow citizens and their society.