There is actually no basic difference among souls except in the degree of their manifestation. All souls possess the same possibilities, whether they are housed in the lowest or the highest form of life.
We have to remember, however, that the Supreme manifests Himself in infinite ways through the different souls. They express His varying aspects of Divinity. For example, one soul may manifest Light, another Power, a third Beauty, and so on.
It is by manifesting their hidden potentialities through the process of reincarnation that some souls have become great spiritual Masters. And all souls shall eventually follow them.