The first mistake Westerners make is to use their own way of thinking about religion to try to understand Islam. Islam is a complete lifestyle that instructs followers every behavior, right down to how to drink water. Actions are either permitted (halal) or forbidden (haram). Followers MUST fully and completely comply, and the word Islam translates roughly to I submit. Islam encompasses law, politics and worship and it is impossible to separate one of these from the other.
It is why their societies are brutal and filthy sh!tholes.