In some religions, it is permissible for non-members to continue being non-members. An example would be Judaism, where non-Jews only have to follow Seven Laws of Noah. In other words, for Jews, it is okay for non-Jews to not practice Judaism as Jews do.
In contrast, Muslims believe that the entirety of their religion is universal and should be followed by all humans. I am currently learning about Christianity. From what I have read, Christians also believe that every human being should be Christian. What are the major Christian viewpoints?