In this article from USA Today, it notes that:
“The percentage. of people who call themselves in some way Christian has dropped more than 11% in a generation. The faithful have scattered out of their traditional bases: The Bible Belt is less Baptist. The Rust Belt is less Catholic. And everywhere, more people are exploring spiritual frontiers — or falling off the faith map completely.”
However, as most of the various forms of groups commonly referred to as Christian by the media really aren’t by the definition the one Christian Church—Catholicism, which increased in the United States & the world—applies to them, according to the teaching clarified by Pope Benedict XVI in 2007.
“Second Question: What is the meaning of the affirmation that the Church of Christ subsists in the Catholic Church?
“Response: Christ "established here on earth" only one Church and instituted it as a "visible and spiritual community", that from its beginning and throughout the centuries has always existed and will always exist, and in which alone are found all the elements that Christ himself instituted. "This one Church of Christ, which we confess in the Creed as one, holy, catholic and apostolic […]. This Church, constituted and organised in this world as a society, subsists in the Catholic Church, governed by the successor of Peter and the Bishops in communion with him".
“In number 8 of the Dogmatic Constitution Lumen gentium ‘subsistence’ means this perduring, historical continuity and the permanence of all the elements instituted by Christ in the Catholic Church, in which the Church of Christ is concretely found on this earth.
“It is possible, according to Catholic doctrine, to affirm correctly that the Church of Christ is present and operative in the churches and ecclesial Communities not yet fully in communion with the Catholic Church, on account of the elements of sanctification and truth that are present in them. Nevertheless, the word "subsists" can only be attributed to the Catholic Church alone precisely because it refers to the mark of unity that we profess in the symbols of the faith (I believe... in the "one" Church); and this "one" Church subsists in the Catholic Church.
“Third Question: Why was the expression "subsists in" adopted instead of the simple word "is"?
“Response: The use of this expression, which indicates the full identity of the Church of Christ with the Catholic Church, does not change the doctrine on the Church. Rather, it comes from and brings out more clearly the fact that there are "numerous elements of sanctification and of truth" which are found outside her structure, but which "as gifts properly belonging to the Church of Christ, impel towards Catholic Unity".
"It follows that these separated churches and Communities, [Orthodox] though we believe they suffer from defects, are deprived neither of significance nor importance in the mystery of salvation. In fact the Spirit of Christ has not refrained from using them as instruments of salvation, whose value derives from that fullness of grace and of truth which has been entrusted to the Catholic Church".
“Fourth Question: Why does the Second Vatican Council use the term "Church" in reference to the oriental Churches separated from full communion with the Catholic Church?
“Response: The Council wanted to adopt the traditional use of the term. "Because these Churches, although separated, have true sacraments and above all – because of the apostolic succession – the priesthood and the Eucharist, by means of which they remain linked to us by very close bonds", they merit the title of "particular or local Churches", and are called sister Churches of the particular Catholic Churches.
"It is through the celebration of the Eucharist of the Lord in each of these Churches that the Church of God is built up and grows in stature". However, since communion with the Catholic Church, the visible head of which is the Bishop of Rome and the Successor of Peter, is not some external complement to a particular Church but rather one of its internal constitutive principles, these venerable Christian communities lack something in their condition as particular churches.
“On the other hand, because of the division between Christians, the fullness of universality, which is proper to the Church governed by the Successor of Peter and the Bishops in communion with him, is not fully realised in history .
“Fifth Question: Why do the texts of the Council and those of the Magisterium since the Council not use the title of "Church" with regard to those Christian Communities born out of the Reformation of the sixteenth century?
“Response: According to Catholic doctrine, these Communities do not enjoy apostolic succession in the sacrament of Orders, and are, therefore, deprived of a constitutive element of the Church. These ecclesial Communities which, specifically because of the absence of the sacramental priesthood, have not preserved the genuine and integral substance of the Eucharistic Mystery cannot, according to Catholic doctrine, be called "Churches" in the proper sense.”