인프런 커뮤니티 질문&답변

package hello.core.member;

public interface MemberService {
    void join(Member member);

    Member findMember(Long memberId);
}

package hello.core.member;

public interface MemberRepository {
    void save(Member member);

    Member findById(Long memberId);
}

에서 findMember, findById객체를 왜 Member타입으로 설정하는 건가요?