How You Can Tell the Difference Between a True Church and a False

… The true mark by which to discern the Church of Jesus Christ [is] to be where his holy Gospel is purely and faithfully preached, declared, listened to and heeded; where the Sacraments are rightly administered, even though there continue to be some imperfections and flaws, as they will always be among men.  On the contrary, where the Gospel is not declared, heard and received, there we recognize by no means the Church. –  John Calvin