Blessed Isaac of Stella writes: The Church can forgive nothing without Christ, and it is Christ’s will to forgive nothing except with the Church. The Church can forgive no-one except the penitent – that is, one who has been touched by Christ – and Christ does not wish to forgive anyone who does not value the Church. What God has united, man must not divide, says Christ, and Paul adds, I am saying that this great mystery applies to Christ and the Church. Do not sever the head from the body so that Christ is whole no longer. For Christ is not whole without the Church, nor is the Church whole without Christ.
If the Church is the bride of Christ, then Blessed Isaac is drawing the conclusion that there is an indissoluble bond between Christ and his Church, and comes up with the radical statement that Christ is not whole without the Church, nor is the Church whole without Christ.
Now it depends how you define ‘Church’. If we mean the invisible church: that is to say, “All baptized people with faith in Christ” then these observations by Blessed Isaac are not very disturbing for we cannot identify this invisible church. As my non Catholic Christian friends rightly observe, “the membership is known to God alone.” If this invisible church is what is being discussed here, then it also follows that “it doesn’t really matter what church you go to as long as you love Jesus”.
However, by virtue of the incarnation, Christ is identifiable. He is not just the ‘invisible Christ who is known to God alone.” He was here present. It happened in time and place. The incarnation plunges us into what the theologians call ‘the scandal of particularity’. That is to say, the outrageous idea that God who is infinite took a particular finite form in place and time.
Nevertheless, this is the claim made by the Catholic Church. “Yes” we say, “there is a sense that the church is invisible and it does include all the baptized who have faith in Christ. However, it is more vital and real in its present and particular manifestation.” We say therefore that the Church ‘subsists’ in the Catholic Church. In other words, you can identify the Body of Christ. It is incarnate in the world, and it’s fullest expression is the Catholic Church.
Last thing: if this is the case, that the Church is the Bride of Christ, then schism is divorce and going from one denomination to another is a kind of spiritual promiscuity. Not good.