Questions & Answers about Мы говорили со священником.
Because after the preposition с / со meaning with, Russian normally uses the instrumental case.
So:
- священник = priest (dictionary form, nominative)
- священником = with a priest / with the priest (instrumental)
This is a very common pattern:
- с другом = with a friend
- с братом = with a brother
- с учителем = with a teacher
So in Мы говорили со священником, the ending -ом shows the instrumental case.
Russian sometimes uses со instead of с to make pronunciation easier.
Here, с св... would be awkward because of the consonant cluster. So Russian prefers:
- со священником
This happens in other expressions too, for example:
- со мной = with me
- со всеми = with everyone
So со is not a different meaning from с here; it is just the smoother pronunciation.