This is the 16513th most frequent Polish word.
wierzącą
Believing (female form).
Here, 'wierzącą' is used as an adjective in the accusative case, describing a person who believes or has faith.
Widziałem wierzącą osobę modlącą się w kościele.
I saw a believing person praying in the church.
Here, 'wierzącą' functions as a noun in instrumental case (derived from adjective) representing a female believer.
Rozmawiałem z wierzącą o jej przemyśleniach na temat wiary.
I talked to a believer about her thoughts on faith.
In this sentence, 'wierzącą' is an adjective in instrumental case describing the intent to be a person of stronger faith.