Christian and Muslims wanted to control the holy land because?

They wanted control over it because it was a "holy land" to both of them: to Christians it was the land where Jesus lived and for the Muslims it's a holy site because it was visited by many prophets, including Muhammad.

They wanted to be sure that they can visit their holy sites without interruption, so they wanted to have control over the land (and they believed that the holy land should be in their hands).