Adrian Fortescue wrote that Leo XIII "begins by explaining again that the ancient Eastern rites are a witness to the Apostolicity of the Catholic Church, that their diversity, consistent with unity of the faith, is itself a witness to the unity of the Church, that they add to her dignity and honour. He says that the Catholic Church does not possess one rite only, but that she embraces all the ancient rites of Christendom; her unity consists not in a mechanical uniformity of all her parts, but on the contrary, in their variety, according in one principle and vivified by it."