Salaam,
Please explain why male Believers are permitted to marry people of the Book (Christians)? Do they not commit shirk?
[2:221] Do not marry the ‘MUSHRIKAAT’ until they believe; a believing slave woman is better than a ‘mushrika’, even if you like her. And do not marry the ‘MUSHRIKEEN’ until they believe. A believing slave man is better than a mushrik, even if you like him. These invite to the fire, while God invites to Paradise and forgiveness, with His permission, and He clarifies His revelations for the people, that they may remember.
salaam