The Prophet only knows what Allah reveals to Him

Re: The Prophet only knows what Allah reveals to Him

one replied monotheism,the religion (deen means religion only naa?) of Ibrahim, and one replied none.
i am confused yaar!
and whats Shariah of Chrisitianity mean??
and if he practised no religion, wont he be called a non-beliver, untill he gained Prohethood??