One is not saved through the church, but saved by grace through faith in Jesus Christ. Elsewhere, the apostles teach that once one has accepted Christ, they are automatically added to the universal church of Jesus Christ (not a visible organization, but the invisible entity known as the Body of Christ). Hence, it is impossible to become saved, and not also become a member of the universal Body of Christ.
However, it is possible to attend a church building on Sundays, or whenever, even join many church organizations, and not be saved.
I've long been upset by people quoting the saying in the Catholic church that, "If you believe the Catholic church to be the true church, but do not practice it's teachings, you will not be saved." That statement is often used to imply that Catholics believe only THEY will be saved. The opposite is the truth! The rest of the statement is that if you believe that the Baptist, Methodist, etc. church is the true church then you won't be saved if you don't follow their teachings. In other words, follow your conscience and you will be saved. Simple as that.
The Mormons also make a statement, "we are the one true church". Which is a bunch of poppy-cock.
The true "church" consists of true believers; be they Methodists, Catholics, Presbyterians, Lutherans, and even us Fundamentalists, etc.
Early Church historian J. N. D. Kelly, a Protestant, writes: "As regards ‘Catholic’ . . . in the latter half of the second century at latest, we find it conveying the suggestion that the Catholic is the true Church as distinct from heretical congregations (cf., e.g., Muratorian Canon). . . . What these early Fathers were envisaging was almost always the empirical, visible society; they had little or no inkling of the distinction which was later to become important between a visible and an invisible Church" (Early Christian Doctrines, 190–1).
.N.D. Kelly, writes in his classic work Early Christian Doctrines (HarperSanFrancisco, 1978) :
"According to him [St. Augustine], the Church is the realm of Christ, His mystical body and His bride, the mother of Christians [Ep 34:3; Serm 22:9]. There is no salvation apart from it; schismatics can have the faith and sacraments....but cannot put them to a profitable use since the Holy Spirit is only bestowed in the Church [De bapt 4:24; 7:87; Serm ad Caes 6]....It goes without saying that Augustine identifies the Church with the universal Catholic Church of his day, with its hierarchy and sacraments, and with its centre at Rome....By the middle of the fifth century the Roman church had established, de jure as well as de facto, a position of primacy in the West, and the papal claims to supremacy over all bishops of Christendom had been formulated in precise terms....The student tracing the history of the times, particularly of the Arian, Donatist, Pelagian and Christological controversies, cannot fail to be impressed by the skill and persistence with which the Holy See [of Rome] was continually advancing and consolidating its claims. Since its occupant was accepted as the successor of St. Peter, and prince of the apostles, it was easy to draw the inference that the unique authority which Rome in fact enjoyed, and which the popes saw concentrated in their persons and their office, was no more than the fulfilment of the divine plan." (Kelly, page 412, 413, 417)
Augustine
"We must hold to the Christian religion and to communication in her Church, which is Catholic and which is called Catholic not only by her own members but even by all her enemies. For when heretics or the adherents of schisms talk about her, not among themselves but with strangers, willy-nilly they call her nothing else but Catholic. For they will not be understood unless they distinguish her by this name which the whole world employs in her regard" (The True Religion 7:12 [A.D. 390]).
"We believe in the holy Church, that is, the Catholic Church; for heretics and schismatics call their own congregations churches. But heretics violate the faith itself by a false opinion about God; schismatics, however, withdraw from fraternal love by hostile separations, although they believe the same things we do. Consequently, neither heretics nor schismatics belong to the Catholic Church; not heretics, because the Church loves God, and not schismatics, because the Church loves neighbor" (Faith and Creed 10:21 [A.D. 393]).
...
""If you should find someone who does not yet believe in the gospel, what would you [Mani] answer him when he says, ‘I do not believe’? Indeed, I would not believe in the gospel myself if the authority of the Catholic Church did not move me to do so" (ibid., 5:6).
In the Catholic Church . . . a few spiritual men attain [wisdom] in this life, in such a way that . . . they know it without any doubting, while the rest of the multitude finds [its] greatest safety not in lively understanding but in the simplicity of believing. . . . [T]here are many other things which most properly can keep me in her bosom. The unanimity of peoples and nations keeps me here. Her authority, inaugurated in miracles, nourished by hope, augmented by love, and confirmed by her age, keeps me here. The succession of priests, from the very see of the apostle Peter, to whom the Lord, after his resurrection, gave the charge of feeding his sheep [John 21:15–17], up to the present episcopate, keeps me here. And last, the very name Catholic, which, not without reason, belongs to this Church alone, in the face of so many heretics, so much so that, although all heretics want to be called ‘Catholic,’ when a stranger inquires where the Catholic Church meets, none of the heretics would dare to point out his own basilica or house" (Against the Letter of Mani Called "The Foundation" 4:5 [A.D. 397]).