If the church were constituted by our faith, then a series of churches would be conceivable, because there are varying views regarding Christ. Luther’s faith in Christ is something different than [sic] that of the modern American Protestant. But if Christ, the present Lord, constitutes the church, then there can be only one church, because there is only one Christ. Then this question is immediately raised: Where does this one church become visible? Where is it knowable for us as a historical reality? And this does not mean for us, Where do we find the people who belong to this church? but rather, Where do we find Christ?
But to this question we can give only one answer: Christ is present for us humans only in the Word and the Sacrament.
Hermann Sasse, ‘Church and Churches: Concerning the Doctrine of the Unity of the Church’, The Lonely Way: Selected Essays and Letters, Vol. I, 82–83. Emph. added