Faith in Christ is Necessarily Ecclesial

...the life of the believer becomes an ecclesial existence, a life lived in the Church. When Saint Paul tells the Christians of Rome that all who believe in Christ make up one body, he urges them not to boast of this; rather, each must think of himself "according to the measure of faith that God has assigned" (Rom 12:3). Those who believe come to see themselves in the light of the faith which they profess: Christ is the mirror in which they find their own image fully realized. And just as Christ gathers to himself all those who believe and makes them his body, so the Christian comes to see himself as a member of this body, in an essential relationship with all other believers. The image of a body does not imply that the believer is simply one part of an anonymous whole, a mere cog in a great machine; rather, it brings out the vital union of Christ with believers and of believers among themselves (cf. Rom 12:4-5). Christians are "one" (cf. Gal 3:28), yet in a way which does not make them lose their individuality; in service to others, they come into their own in the highest degree. This explains why, apart from this body, outside this unity of the Church in Christ, outside this Church which — in the words of Romano Guardini — "is the bearer within history of the plenary gaze of Christ on the world"[16] — faith loses its "measure"; it no longer finds its equilibrium, the space needed to sustain itself. Faith is necessarily ecclesial; it is professed from within the body of Christ as a concrete communion of believers. It is against this ecclesial backdrop that faith opens the individual Christian towards all others. Christ’s word, once heard, by virtue of its inner power at work in the heart of the Christian, becomes a response, a spoken word, a profession of faith. As Saint Paul puts it: "one believes with the heart ... and confesses with the lips" (Rom 10:10). Faith is not a private matter, a completely individualistic notion or a personal opinion: it comes from hearing, and it is meant to find expression in words and to be proclaimed. For "how are they to believe in him of whom they have never heard? And how are they to hear without a preacher?" (Rom 10:14). Faith becomes operative in the Christian on the basis of the gift received, the love which attracts our hearts to Christ (cf. Gal 5:6), and enables us to become part of the Church’s great pilgrimage through history until the end of the world. For those who have been transformed in this way, a new way of seeing opens up, faith becomes light for their eyes.

-- Pope Francis, Lumen Fidei