Answer: We study three main sources of the wisdom of Kabbalah: The Book of Zohar, the writings of the Ari (mostly his book The Tree of Life), and the works of Baal HaSulam, the great Kabbalist of the 20th century. Baal HaSulam handed down the entire wisdom of Kabbalah to us in the form most suitable for its publishing and distributing to everyone in the world.
Among all the great Kabbalists, starting with Babylon and to this day, each generation produced many other Kabbalists. But some of them concealed themselves and others wrote very little since until very recently, just thirty years ago, to reveal any part of Kabbalah, one had to receive special permission from Above. Hence, Kabbalists rarely wrote and when they did, it was in a secret form.
And only in the 20th century, when the time has come for the revelation of Kabbalah to everyone so as to correct the collective ego, Baal HaSulam wrote what was permitted to distribute. And we are offering this specific part of Kabbalah to the world.
From the Lecture in Rome 5/20/2011