Ibur has similar limitations [as gilgul].

In the previous section we learned that a group of Nefashot from the same root may come together into one body, but there is a quantitative limitation to this possibility. More than four nefashot may not reincarnate together. Of the four, three are reincarnations and one is a new Nefesh. The same quantitative limitation applies to ibur as well.

Up to three Nefashot can come to help a person's Nefesh. The total will then be four. More is not possible, but less is.

However, those who had come in the secret of gilgul only came to help themselves, to rectify their sins, or to fulfill a mitzva they had yet to perform.

The soul of a tzadik may come for its own benefit or only for the benefit of the host

The last section focused on the subject of multiple gilgulim. Now we are beginning the discussion of ibur, and the Rav is reminding us here of the contrast between gilgul and ibur. In gilgul the Nefashot all come at the time of birth, and they all come to benefit themselves, to rectify some sin or perform some mitzva. In contrast, in ibur the soul of a tzadik comes into the host at the age of thirteen and one day, or later. They may come for their own benefit or only for the benefit of the host.

Expanding upon the discussion of ibur, the following is an example.

Consider a person who has reincarnated into a body to rectify himself. He has ten Nefashot in his root that are higher than himself. If he merits it, then the tenth, lowest Nefesh, which is still higher than he is, will enter him as an ibur and help him to achieve tikun. If he increases his merit then he will receive the ninth Nefesh as an ibur, and if he merits more, then the eighth Nefesh will enter. Thus, he will have received three Nefashot, and, including his own, there will be four in total. More than this is not possible.

However, if he further increases his merits, then he can even receive the seventh Nefesh as well, causing the tenth Nefesh to surrender its light to the three higher iburim.

There can only be four Nefashot in the body at one time. One is the host, and three are iburim [plural form of ibur]. If the fourth Nefesh above the host enters, then the lowest of those above the host must leave.

This is the way it continues until he achieves the three highest Nefashot of the ten: the first, second, and third. The light of these three will be revealed in this ibur to assist him. The other seven will lose their light to them; in contrast to the light of the three upper Nefashot, they will seem as if they no longer exist. This is because only three Nefashot, in addition to the Nefesh of the person himself, are possible [in one gilgul].

[Commentary by Shabtai Teicher.]