They were monotheistic. Being monotheistic means you believe in one god. Their holy book was the bible. Their holy land was Jerusalem. Their holy day was Sunday, the day they went to church.
They thought they were cannibals. They drank wine, thinking it was blood. Romans were polytheistic. Being polytheistic means you believe in more than one god.
The church always has the power. The church had all knowledge. The church says certain rules, you follow them. If you don't follow the rules or you question the church then it will not lead you to heaven, it will lead you to hell.
The crusades always used trade. It was a holy war between Christians and Islam's. It occurred in Europe and the Middle East. They didn't accomplish anything militarily, only trading goods.