Background sources like encyclopedias can provide context for your topic, or even help you choose one. They are great places to start because:
The following are recommended encyclopedias in your field. You can read them online 24/7.
Dictionary of Modern Theological German
by
Helmut W. Ziefle
Das Grosse Wörterbuch der deutschen Sprache
by
Gunther Drosdowski; Dudenredaktion (Bibliographisches Institut), Wissenschaftlicher Rat Staff (Contribution by); Duden Staff (Contribution by)
Deutsches Woerterbuch
by
Hermann Paul; Heidrun Kämper (Editor); Georg Objartel (Editor); Helmut Henne (Editor)
The Oxford-Duden Pictorial German-English Dictionary
The New Cassell's German Dictionary
by
Harold T. Betteridge (Foreword by); Karl Breul (Foreword by)