Room 1408, it actually like in Mike's own mind filled with the subject in the past, he's trying to make it be like Mike, trapped in the mind of the idea, which has the power to 1408 mental torture of persons.
Indeed, in 1408, he is like a room in Mike's own mind is filled with stories of the past. He tried to accept it as if Mike was put in mind of their own ideas, which in 1408 had the power to torment the minds of those who stay.