AFTER the Renaissance, the Reformation. Last week Mr. Somervell described that movement towards worldliness — in the different forms in which it attracted a Botticelli, an Erasmus or a Machiavelli-that broke up medieval Christendom into the beginnings of modern Europe. This evening he will talk of the irruption of certain manifestations of the modern spirit into the religious sphere, resulting in the Reformation and the Counter-Reformation, with such protagonists as Luther, Calvin and Ignatius Loyola , arrayed on either side.