Entry of Nefesh, Ruach & Neshama throughout Life
When a person is born, his Nefesh enters him. If he is adequately rectified through his actions, his Ruach will enter him at the end of his thirteenth year when he becomes a "completed person." His Neshama will enter him only when he completes his twentieth year, as it says in the Zohar (Mishpatim 94b).
This is talking about the ideal situation during a person's first gilgul, as we will soon see.
However, if he does not completely rectify his Ruach, then the Neshama will not enter him and he will remain with only his Nefesh and Ruach. Likewise, if he doesn't completely rectify his Nefesh, then he will remain with only his Nefesh, lacking both his Ruach and Neshama. The Ruach and Neshama will remain in a place known to The Holy One, Blessed is He, and there a place will be prepared for each one.
In other words, until a person is able to receive all parts of his soul, the parts he has yet to receive remain hidden away by G‑d until the person is ready for them.
He will have to die and return in order to receive the Ruach
Now, if a person does not completely rectify his Nefesh the first time and dies, then his Nefesh will have to reincarnate, perhaps even many times, until it is sufficiently rectified. However, since he only achieved tikun through a gilgul, even after complete rectification is achieved his Ruach will not enter [unless there is a pressing need, as will be explained, G‑d willing].
Had it been his first gilgul, then he could have received his Ruach while still alive in his original body. This is not the case if the rectification of the Nefesh is completed during subsequent gilgulim.
He will have to die and return in order to receive the Ruach. Furthermore, once the Ruach is sufficiently rectified, then he will also have to reincarnate before receiving a Neshama, as was the case with the Ruach.
After he finally rectifies his Nefesh and dies, in the next reincarnation he will return with a Nefesh and a Ruach. Once the Ruach is rectified as well, then he will die and come back in another gilgul with a Nefesh, Ruach, and Neshama.
If the Ruach is not sufficiently rectified, then the Nefesh and the Ruach will have to come back again, perhaps many times, until the Ruach is rectified. Once rectification is achieved, then the person will die and his Nefesh and Ruach will come back with the proper Neshama until all three are rectified. Once this is done, there is no need for any further gilgulim. When his Neshama is completed, he has become a "complete person."
[Commentary by Shabtai Teicher.]