Question: In the physical world a rich person has a large fortune. What I get from spirituality, I get from the friends?
Answer: Your spiritual wealth is determined according to how much you can fulfill others. This is what is called “buying” from the friends.
Your purchase remains outside of you. But you also go outside of yourself. Your desire to bestow to them is called your spiritual Kli. And what you attract through this Kli, by fulfilling the friends, is called Light. You move yourself entirely outside. And this is called your spiritual acquisition. The spiritual Kli is not found inside of you.
From the 4th part of the Daily Kabbalah Lesson 3/25/14, Writings of Baal HaSulam