After graduating the Defense Language Institute (DLIFLC), then three years working a live mission, and then graduating the Foreign Language Training Center Europe (FLTCE), I was asked to provide real-time translations from English into Russian for church services for political refugees in West Germany who had defected from the East.
I thought that I was pretty darn good with the live mission vocabulary, but my self-confidence in the language completely evaporated when I realized that I knew absolutely zero of church-related vocabulary in Russian. For instance, I didn't know basic verbs like "pray" or "baptize," or basic nouns like "angel," "salvation," "altar," etc. I didn't even know the name of books in the Bible like "Римлянам," "Второзаконие," "Деяния," etc.
Yup - I quickly realized that when it came to church vocabulary, I was a totally worthless n00b.