Luther's Works is a large set of books that contains Luther's sermons, commentaries, theology, etc. Use the table of contents listed in each link below to help you determine which volume you would like to consult.
Use these resources to find primary sources - sermons, writings, etc. - on your topic.
In addition to the websites above, you can often find primary sources in books. Use OneSearch (below) to search for books in the library's collection. Consider adding one of these keywords to help find books that contain primary sources: