Church as a religious group?

The famous German theologian Ernst Käsemann wrote:

"[Paul] the apostle is not interested in the church per se and as a religious group. He is only interested in it as far as it is the means whereby Christ reveals himself on earth and becomes incarnate in the world through his Spirit." (Perspectives on Paul. Translated by Margaret Kohl. Philadelphia; Fortress, 117)

Isn't that going a bit far? Doesn't this present an un-Pauline either/or?

But Käsemann's distinctions raise another interesting question: Does 'Christ reveal himself on earth and become incarnate in the world through the Spirit' outside the religious community?

If so, then in what sense is the Church the 'body of Christ' if it fails in this task? And what counts as failure? Does it then cease to be the Church? Is Augustine's distinction between the visible and invisible Church the only option?