Islam started strangely to the Arabs in Mecca, despite the fact that it doesn’t look strange to mankind, because the Prophets of Allah (SWA) were Muslims, but their doctrines were different due to the people that the Prophets were sent to.
The reason why it came strangely was that people were diverted to idol worshipping during absence of prophecy after Prophet Isa left. The people of Mecca had many idols that they were worshipping and also thought that the idols can bring them closer to Allah (SWA).
They gave rules and regulations by themselves, without being inspired by Almighty Allah (SWA), they make sacrifices for the idols and bow to them, and think they can deliver them from any problem they’re facing.
They believed that, god can be made up from any item, and can be made ‘carryable’ so that it’ll be able to prevent them from evils.
They took many gods and worshipped them throughout the year.
They also had different behaviors that were not good, like burying their daughters alive, and inheriting their father’s wives after their death.
When Islam came, it condemned their acts and stopped them from worshiping idols, or having different gods. But the Arabs wondered about the preaching.
Islam is not strange to the nature of mankind, because it’s the religion Allah (SWA) is pleased with, and it the religion preached by the Prophets starting from Prophet Nuh to the last Prophet Muhammad (SAW).
What’s not attached to Islam must not be attached to it by anyone, and there’s no how no one can be called Muslim unless if has believed in what the Prophets brought.
Allah (SWA) used to send and raise those that will call to the real Islam in every country and every time, so that people will not believe in what they should not believe in.
Allah (SWA) sent all the Prophets to their people to guide them from believing in nonsense, or from wrong path. The reason for that is that when people are away from hearing the truth, or learning the righteousness, they’ll be carried away by wrongdoers.