Jesus Christ established one Church with one set of beliefs, as stated in Ephesians 4:5. He did not establish numerous churches with contradictory beliefs. To see which is the true Church, we must look for the one that has an unbroken historical link to the Church of the New Testament.
John Henry Newman, in his 1844 book “An Essay on the Development of Christian Doctrine”, traced Catholic beliefs backward century by century to the New Testament times. He discovered a real continuity of beliefs, that the Catholic Church existed from day one of Church history, that it is in fact the Church established by Christ. Newman was not a Catholic when he started the book, but his research convinced him of the truth of the Catholic faith and as the book was finished he converted.