Here this refers to fellow Christians including males and females. Alternate translation: "brothers and sisters" or "fellow believers" (See: [[rc://en/ta/man/translate/figs-metaphor]] and [[rc://en/ta/man/translate/figs-gendernotations]])
Here "heart" is a metonym that represents a person's mind or will. Refusing to believe and obey God is spoken of as if the heart did not believe and it physically turned away from God. Alternate translation: "there will not be any of you who refuse to believe the truth and who stop obeying the living God" (See: [[rc://en/ta/man/translate/figs-metonymy]] and [[rc://en/ta/man/translate/figs-metaphor]])