Consider that Paul, the inspired author of most of the epistles, having seen the glorified Body of Christ, knowing what end Christ’s body finally meets, and presumably knowing about what language Christ uses about his body throughout the Gospels, uses this specific metaphor: the Church is the Body of Christ.
What could such a metaphor really mean? If it is true, and if it is scriptural, and if it is inspired — full of the Spirit — surely it has at least a divine meaning and purpose. It must speak to some deeper principle. Catholics may point out that Christ will not die, now that the Resurrection shows He triumphs over death. Similarly, the Body of Christ will, in some visible way on this earth, live right up until the end times.
Catholics also may explain this as affirming the four marks of the Church. Like Christ’s body, Catholicism is one, a matter disputed principally by log-eyed men. She is holy, for the Church Triumphant is in heaven and the Church Suffering is headed there, however the visible Church Militant fails us. She is Catholic, which is a word that means simply universal. That the Church is apostolic is simply a way of saying her authority goes back to the apostles, which is important not because of the apostles but because of Christ. There is a real historical claim backing each of these up, putting aside doctrine and scripture, claims which have no analogue among apostasists.
I am curious what apostasists make of this passage on their own, not just what other verses they go to to defend against this interpretation. All I can think of is what apostasists cannot say.