Humans possess several different souls. The first of these, the vital soul, is purely vegetative. The second is more highly evolved and is known as the animal soul; the third is the sensitive or emotional soul; the fourth is known as the rational or reasonable soul, and, finally, there is the divine soul, the soul of pure light, possessed only by initiates who have completed their evolution.
The most basic, the vegetative soul, enters and animates the embryo while it is still in the womb.
At the age of seven children receive their animal or voluntary soul. The belief that at this age, the ‘age of reason’, children enter into full possession of their soul is a very common error. No, the fact is that the soul they receive is still only the voluntary or animal soul. From the time they are born, children are constantly in motion, moving their arms and legs, walking and running and jumping about, and by the time they are seven and their animal soul has fully entered their body you could say that they have acquired sufficient physical autonomy to be in control of their movements.
For some time before this however, a new phase has begun, the phase during which the affective dimension becomes gradually more important: the sensitive or emotional soul has begun to develop. At about fourteen, when children reach puberty, the sensitive soul reaches maturity and enters fully into them, leading them to give priority to their emotions.
At the same time the capacity for reflection begins to develop and, at the age of twenty-one, the intellectual or rational soul enters fully into a human being.
As for the divine soul, its coming depends entirely on the kind of life we have chosen to live and on our desire to receive it.
Initiation is just that, the path human beings tread in order to seek out their divine soul and persuade it to take up permanent residence in them.
In fact, though, only a few very exceptional beings who have spent many incarnations working for this goal actually achieve it.
For years and years, by means of their spiritual exercises of purification, meditation, prayer and sacrifice, they have prepared themselves to attract and become one with their higher self, their divine self. And when they attain their goal we say that they have received the Holy Spirit.
Omraam Mikhaël Aïvanhov
Izvor Book 222, Man’s Psychic Life, Elements and Structures,
Chapter 3, Several Souls and Several Bodies