Answer: Selling your soul to the devil means giving all your desires for money and even for knowledge in our world. Everything in our world is called the “devil” because all our corporeal engagements divert us from the spiritual path. The world “devil,” “Satan,” stems from the Hebrew root “Leastin” (to divert). It refers to any engagement in our world by which a person replaces his yearning for the true goal.
From the Kabbalah Lesson in Russian 4/3/16