Two schools of economics / religion (behavioural / neoclassical, islam / christianity) with many shared assumptions (similar holy texts) that have attracted followers due to offering common sense advice and a solid framework of practical value but pursue an ongoing holy war over certain doctrinal issues that are equally flawed and ungrounded in reality.

Or: what they agree on is largely wrong but has some instrumentally useful elements. What they disagree on is largely irrelevant. The priesthood considers the differences very significant but most people ignore everything but the useful bits and get on with their lives.