What are the differences between the religions of Christian and Muslim in the crusades?

Big difference...

1. They were, and still are, completely different religions

2. the main cause of the whole Crusade was the clash between the 2 religions.

3. Simple as this: in those times, the Christians despised the Muslims and vice versa.

The Crusades started because the Muslims had taken control of the city of Jerusalem, the birthplace of Christianity (and also the early home of the prophet Mohammed). They raged on for 200 years.