But the one thought which is ever constant with him, and is peculiarly helpful to the practical man, is his recognition of the value of limitation in all our energies, and the stress he lays on the fact that only by virtue of this limitation can we grow. We should be paralysed else. It is Goethe's doctrine of _Entbehrung_, and it is vividly portrayed in the epistle of Karshish. Paracelsus learns it, and makes it clear to Festus at the end. The natural result of Browning's theory of evil, and his sense of the value of limitation, is that he should welcome for man the experience of doubt, difficulty, temptation, pain; and this we find is the case. Life is probation and the earth no goal But starting point of man ... To try man's foot, if it will creep or climb 'Mid obstacles in seeming, points that prove Advantage for who vaults from low to high And makes the stumbling-block a stepping-stone. _The Ring and the Book_: The Pope, 1436-7, 410-13. It is this trust in unending progress, based on the consciousness of present failure, which is peculiarly inspiriting in Browning's thought, and it is essentially mystical. Instead of shrinking from pain, the mystic prays for it, for, properly met, it means growth. Was the trial sore? Temptation sharp? Thank God a second time! Why comes temptation but for man to meet And master and make crouch beneath his foot, And so be pedestaled in triumph? _The Ring and the Book_: The Pope, 1182-02.