-Holy people who know the mysteries of Kabbalah are able to meditate and do great Yichudim causing mass unifications in the spiritual realms.
-A person can only bind himself to the root he stems from, therefore his unifications will be limited to that area.
-These unifications help the overall rectification of the world, they also help the person advance through the varies levels.
-There are specific openings in time when a person can unify all the roots together. A person must know exact time, as well as the meditations needed to enter this opening.
-Only the greatest Kabbalists were able to reach this level, of being able to unify all the roots. The rest of the sages were only able to cause such unification at the time of their death.
-Binayahu ben Yehayada was one of the Kabbalists that reached this level.
-That is why he is called ‘son of living man’ (Ben Eish Chi) since he was able to unify all the roots while he was still alive, as opposed to others who were only able to do so at the time of death.
-That is why he is referred to as the ‘gatherer’ (Mikavziel) since he was able to gather and unify all the worlds.
-When a person properly meditates on a great Yichud the sprit of Benayahu ben Yehayda will sometimes come down and accompany him, since Benayahu was busy with this his whole life.

(Kitvi Ari, Shar Roach Hkodesh Inroduction 1 to Yichudim)