When Pope Pius X, standing upon the traditional rock of papal authority, issues a decree upon matters of faith, his words carry the weight not only of his sacred office but also of his immense social influence. We may perhaps share Tertullian's amazed indignation, when Pope Calixtus first assumed the right to speak for the whole church—“Audio edictum esse praepositum et quidem peremptorium”—and yet we listen. We listen, because, in this modern world, no interest which concerns the well-being of any part can be of indifference to the whole social structure; and more especially we listen because the movement which in Roman Catholic circles is known as Modernism is a vital and pressing problem in every organized body of Christian believers.