"There is more to the affinity between magic and existentialism than the celebration of a common hero (Satan). The very picture of self-discovery which is painted for us in books on Hermetic Philosophy and the Cabalah can also be found in the writings of Heidegger and Sartre. The magus, like the existentialist, embarks upon a search for authenticity to a confused and troubled worry. The obstacles which confront him on his journey are chiefly the temptations to participate in partial and, therefore, inauthentic existence. In the end, he arrives at an awareness of the absolute nature of his freedom. The journey is the same; only the landmarks differ."
"The will is the link between man and the world. Only through the will can man actualize his freedom. Will is not a quality which can be understood apart from action; it is, in effect, freedom realized in action. Of course, the will can lie dormant or be realized in inauthentic activity. In such instances, it is again expressive of one’s state of being. Existentialism, obviously, encourages active willing because it encourages the authentic realization of one’s freedom, something which cannot be accomplished without the participation of the will...
"The importance of the will in magic is equally profound. For the magus, will is the means by which he successfully achieves his magical project. All failures in magic are attributed to the failure of the will. The will is both the means by which the magus opens himself to the future magical possibilities and the necessary magical ingredient for the attainment of short-range goals. 'Do what thou wilt shall be the whole of the law,' was Crowley’s magical motto. 'What is a magical operation?' wrote Crowley. 'It may be defined as any event in Nature which is brought to pass by Will. We must not exclude potato-growing or banking from our definition.'"
Both quotations are from an unpublished mss, The Spectre in the Lake: Magic past and future by Dan Wick.