And I must inform you of the concept of the ORDER of ibur in more depth. [To do this, I will] give an analogy: Say, a person exerts himself to rectify himself when he is in this gilgul in this body. Let's say he has in the source of his souls ten other Nefashot which are at a higher level than he is. If this Adam merits, he can have the 10th [the lowest of the ten Nefashot which are higher than him] Nefesh enter into him in the form of an ibur, and it [the 10th lowest Nefesh] is higher than him.
This 10th lowest Nefesh helps him and lifts him, and if he merits further, he can receive the 9th lowest Nefesh (as a second ibur). And if he merits further, the 8th lowest Nefesh can enter into him (as a third ibur), and thus he has received three Nefashot which have entered into him as an ibur [the 10th, the 9th, and the 8th,] so counting him, there are four [Nefashot], and it is not possible for more to 'ibur' into him.
But if he merits further, the 7th Nefesh can 'ibur' into him; if this happens, the 10th lowest Nefesh will be nullified as an ibur (it will not be considered as the three Nefashot who are entering into him as an 'ibur' [because the 10th lowest Nefesh no longer helps him, but it is not disconnected from him, and it still gets the benefits from his Torah and mitzvos]). And this is the way it continues until he reaches the top three of the ten highest Neshamot, and they are the 1st, the 2nd, and the 3rd.
These are the three that reveal influence to him to help him, and the other seven's influence is nullified due to the greater influence of the higher three Neshamot. You might think that they are as if they are not there (but they do not leave completely); they are just unable to reveal (light) to him through the secret of ibur, because only three Nefashot can enter into him only, and with his own Nefesh, this is four Nefashot. But more than this -- it is not possible, as we already described.