"Orthodox Judaism is a thicket of detailed injunctions, Biblical commandments elaborated during centuries of prohibited proselytizing, functioning to limit interaction with outsiders. At the opposite extreme, Islam, still the most rapidly expanding of faiths, demands little immediate knowledge from those who would convert. The convert is permitted to enter and then to learn by participation, although there are plenty of detailed regulations and abstruse theological ideas to be pursued later, and the regulations do effectively separate believers from nonbelievers."