The third mark by which the true Church of Christ can be identified is Catholic or universal. The Church is universal in time, place, and doctrine. She is not confined to one nation or one class of people.
The Roman Catechism: “She is also called universal, because all who desire eternal salvation must cling to and embrace her, like those who entered the ark to escape perishing in the flood. This (note of catholicity), therefore, is to be taught as a most reliable criterion, by which to distinguish the true from a false Church.”
Pope Eugene IV, Council of Florence, Cantate Domino: “The Holy Roman Church firmly believes, professes and preaches that all those who are outside the Catholic Church, not only pagans but also Jews or heretics and schismatics, cannot share in eternal life and will go into the everlasting fire which was prepared for the devil and his angels, unless they are joined to the Church before the end of their lives.”
Pope Leo XIII, Satis Cognitum #9: “The practice of the Church has always been the same, as is shown by the unanimous teaching of the Fathers, who were wont to hold as outside Catholic communion, and alien to the Church, whoever would recede in the least degree from any point of doctrine proposed by her authoritative magisterium…But he who dissents even in one point from divinely revealed truth absolutely rejects all faith, since he thereby refuses to honor God as the supreme truth and the formal motive of faith… The Church alone offers to the human race that religion – that state of absolute perfection – which He wished, as it were, to be incorporated in it. And it alone supplies those means of salvation which accord with the ordinary counsels of Providence.”
A church that claims that salvation can be attained elsewhere is obviously missing the third mark. A church that declares that it has the fullness of means of salvation but other deficient religions are a means of salvation most definitely does not possess the third mark.
Speray's Catholicism in a Nutshell 