Question: If friends have a desire to work together, how can we help them reveal a deficiency (Hissaron) for spirituality?

Answer: Read about this in the ten before or after our lessons so they can hear and see where you are getting these articles from. Engage them.

Question: Group work is clear, but can individual work with the sources help? Is it necessary, and what is its importance?

Answer: Individual work with the sources is effective when you get explanations of what is written in them.

If you do not know and are just guessing, it will not help you much.
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From the Daily Kabbalah Lesson 7/31/24, Writings of Rabash “The Torah Is Acquired through Suffering”

Related Material:
The Correct Attitude Toward The Sources
The Main Rule For Reading Kabbalistic Books
Reading A Kabbalistic Text