Here are 3 definitions of the soul from The Spirit's Book / Introduction by Allan Kardec:

"There is another word of which it is equally necessary to define the meaning, because it is the keystone of every system of morality, and also because, owing to the lack of a precise definition, it has been made the subject of innumerable controversies; we refer to the word soul. The divergence of opinion concerning the nature of the soul is a result of the variety of meanings attached to this word. A perfect language, in which every idea had its own special term, would save a vast deal of discussion; for, in that case, misunderstanding would be impossible.

Some writers define the soul as being the principle of organic life, having no existence of its own, and ceasing with the life of the body. According to this purely Materialistic belief, the soul is an effect, and not a cause.

Others consider the soul as being the principle of intelligence, the universal agent, of which each being absorbs a portion. According to them, there is, in the entire universe, only one soul, which distributes sparks of itself among all intelligent beings during their life; each spark, after the death of the being it has animated, returning to the common source, and blending again with the general whole, as brooks and rivers return to the ocean from which they were produced. This opinion differs from the preceding one, inasmuch as, according to the latter hypothesis, there is in us something more than matter, something that remains in existence after our death; but, practically, it is much as though nothing remained of us, since, no longer possessing individuality, we should retain no consciousness of our identity.

According to this hypothesis, the universal soul is God, and each being is a portion of the Divinity. It is a species of Pantheism.

According to others, again, the soul is a moral being, distinct, independent of matter, and preserving its individuality after death. This acceptation of the word soul is certainly the one most generally received; because, under one name or another, the idea of a being that survives the body is found as an instinctive belief, and independently of all teaching, among all nations, whatever their degree of civilization. This doctrine, according to which the soul is a cause and not an effect, is that of the spiritualists."

These are very interesting definitions. My understanding of the soul is closest to the third one but also includes some elements of the second definition.

Soul means a matrix of all activities, all activities originate from the soul. What does it mean in practice? Soul prepares a program before taking birth. It includes all the key points or goals for the next life and that means all achivements are being prewritten in that program.

Soul does not know how it will get from point A to point Z in life. The path depends on the free will. Just like in life we have a choice to use a train, a bus, our car or we choose to walk to get to our destinations. Similarly, a soul will make choices in life to move from one goal to another. The choices may not always be the easiest or the fastest paths possible but surely always right for that soul.

Summerizing, once soul is born, it follows the program but it forgets about writing it. Free will is only within HOW we get from one point to another in our life, not IF we get there, it does not affect the goal itself.