Physician

Question

Is it consdered a mitzvah to become a physician? I know saving a Jew's life i a mitzvah, but how about a goy? Is there any mitzvah to save his life? Lastly, even if it is a mitzvah to save a goy, the average goy in America is a Christian. Aren't Christians Ovdei Cochavim, and thus it would not be a mitzvah to save them anyway? These questions are important because it will determine what profession I will choose to take up. Thank you very much, and looking forward to your response!