Complex sentence: More importantly, it officially exempted the church from any form of taxation by Mongol or Russian authorities and permitted that clergymen not be registered during censuses and that they were furthermore not liable for forced labor or military service.
Split into simpler sentences: More importantly, it officially exempted the church from any form of taxation by Mongol or Russian authorities. And permitted that clergymen not be registered during censuses and that they were furthermore not liable for forced labor or military service.