Is the Foundations of Christianity relevant at all? I think it's basically just Kautsky trying to apply historical materialism (HM) to a real-world situation. From what I know -- and I could be quite wrong here, because I'm a bit of a Kautsky noob -- Kautsky takes the position that, to understand HM, you also need to have an understanding of, or base yourself in, the materialist dialectic (DM). Yet people like Rosa Lichtenstein say that we should scrap DM altogether and just focus on HM, but I don't think it's that simple, because both theories are inter-connected, and knowing one will help your understanding of the other, or vice versa. Does this make sense? I suggested this also because I saw a copy of it in the CWI bookshop :P