Why do Catholics believe that their Church is the one true Church of Jesus Christ? Wouldn’t it be more reasonable to believe that Christ’s true Church is a spiritual union of all Christian denominations?
Catholics believe that theirs is the one true Church of Jesus Christ, firstly, because theirs is the only Christian Church that goes back in history to the time of Christ; secondly, because theirs is the only Christian Church which possesses the invincible unity, the intrinsic holiness, the continual universality and the indisputable apostolicity which Christ said would distinguish His true Church; and thirdly, because the Apostles and primitive Church Fathers, who certainly were members of Christ’s true Church, all professed membership in this same Catholic Church (See Apostles’ Creed and the Primitive Christian letters). Wrote Ignatius of Antioch, illustrious Church Father of the first century: “Where the Bishop is, there let the multitude of believers be; even as where Jesus is, there is the Catholic Church.” Our Lord said: “There shall be one fold and one shepherd”, yet it is well known that the various Christian denominations cannot agree on what Christ actually taught. Since Christ roundly condemned interdenominationalism (”And if a house be divided against itself, that house cannot stand.” Mark 3:25), Catholics cannot believe that He would ever sanction it in His Church.
Mary and the “Saints” are simply dead people, they have no more power than YOU and I do.