The most important condition for studying The Book of Zohar is a well-prepared, organized group. You cannot open The Book of Zohar alone and expect it to begin to influence you and to reveal the upper world to you. You need to be in a certain connection with the friends for that to happen.
When a person studies The Book of Zohar with the friends, he spurs and summons changes to the point that he begins to feel the picture of the upper world in the connection like on a TV screen: sensations, volumes, dependencies. There cannot be any feeling of the upper world unless you are connected to the group.
In our world there is no connection between people. We are absolute egoists who aspire only to extract mutual benefit from each other. And in the upper world this connection is revealed during the study of The Book of Zohar, and a person begins to actually perceive, explore, and affect it.
The Book of Zohar does not require prolonged effort, especially not mental ones. The efforts should be emotional. You should study regularly, but not for a long time. An hour a day is enough.
From the Kabbalah Lesson in Russian 2/12/17