Translation:The priest of our church is Daniel.
The priest OF our church sounds clumsy and you wouldn't hear it normally in spoken english. AT our church is what you'd hear.
The possessive adjective agrees in case with the noun (here, the genitive case). It just so happens feminine words in the genitive/dative form have the same singular form as in the nominative/accusative plural.
''Daniel is the priest of our church'' should also be correct, no? It's arguably more natural to say in English, as opposed to 'The priest of...'