[T]he Church is Catholic from her first moment, her universality is not the fruit of the successive inclusion of various communities. From the first instant, in fact, the Holy Spirit created her as the Church of all peoples; she embraces the entire world, she transcends all limits of race, class, nation; she breaks down every obstacle and brings all men together in the profession of the One and Triune God. From the beginning, the Church is One, Catholic, and Apostolic: this is her true nature and as such it must be recognized. She is Holy, not thanks to the ability of her members, but because God Himself, with His Spirit, creates, purifies, and sanctifies her always.
This excerpt is evocative of the clear words of Mortalium Animos, the encyclical letter of the great Pope Pius XI on Christian Unity. Rather than suppose that the Church is not one until and unless there is a reconciliation of various denominations, the Pope described the inherent unity of the Church and her right relation to these groups in words. I quote below in some length, but without footnotes: