There were plenty of books of mysticism during the middle ages and the zohar brings a lot of them. that i why and how Rav Yaakov Emden [the Yaavatz] explains the Zohar. He says some parts of it are from authentic writings of ancient mystics before the time of Moshe Deleon. So while I am not in favor of learning the Zohar, I am in favor of learning the Ari [Isaac Luria].who concentrates on the parts of the Zohar that were ancient teachings. But that is only in connection with Gemara and Tosphot