In spite, however, of this fundamental difference in tone, the wider our reading the more clearly we must realize the extent to which the Christian mystics are conscious or unconscious disciples of Plotinus. That unity of witness which is one of the most impressive facts in the history of mysticism, may reasonably be regarded as evidence of the reality of that world of spiritual values which contemplatives persistently describe. But on its literary side, this same unity of witness depends closely upon the fact that these contemplatives, however widely separated by time and formal creed, were able to make plain their adventures to other men by means of conceptions drawn from the Plotinian scheme; which has proved itself able to rationalize and find room for the deepest spiritual intuitions of man. It could do this because a great mystic made it. Hence we find it implied, even where unexpressed, in many of the masterpieces of later mysticism—both Christian and Mahomedan—and some knowledge of it is a necessary clue to the full understanding of these writings. The Sūfi ’Attar, describing the soul’s arrival in “the Valley of Unity where it contemplates the naked Godhead,” is equally its debtor with the Protestant mystic William Law, declaring that “everything in temporal nature is descended out of that which is eternal, and stands as a palpable visible outbirth of it; so that when we know how to separate the grossness, death, and darkness of time from it, we find what it is in its eternal state.” Yet few of the theologians and contemplatives who owe most to Plotinus had any first-hand acquaintance with the Enneads. Their influence reached the mediæval world by two main channels. The first line of descent is through the works of Victorinus and St. Augustine; the second through the philosopher Proclus and his mysterious disciple Dionysius the Areopagite. These lines meet in the _Divina Commedia_, which may be regarded in one aspect as the supreme poetic flower of Neoplatonism.