A Ladder to the Hidden Treasures
Rav Ashlag explained why he named his commentary on the Zohar the Sulam, the Ladder. A person may have an attic filled with precious jewels, he said. All he needs is a ladder to reach them. The Zohar is that attic of treasures, and the commentary is the ladder that lets a student climb up and reach what is stored there.
Source: Introduction to the Sulam on the Zohar