The modern definition and usage of this word "soul" is filled with contradictions, misconceptions, and misuse. In Gnosis (the heart of all religions), the meaning is very precise. The English word comes from the Old English sawol, meaning the "spiritual and emotional part of a person."
In Kabbalah, the spiritual and emotional part of the person is related to the sephiroth Hod (emotion), Netzach (mind), Tiphereth (will; Human Soul), and Geburah (consciousness; Divine Soul). Furthermore, these sephiroth undergo stages of growth, explained as five types or levels of soul: nephesh, neshemah, ruach, chaiah, and yechidah.
In Hinduism and Buddhism, the word soul is usually related to the Sanskrit word Atman, defined as "self." (See Atman for more information). Yet, this word has been misinterpreted for centuries.
The teaching of the Buddha explains that there is no "soul" in the sense of a permanent, eternally existing element beyond the body that defines a person. Samael Aun Weor uses the word soul in the way that Buddhism uses the word "body" (of which there are physical and nonphysical bodies); each, even when created and refined, is merely a vehicle, and as such is impermanent. What is eternal is what uses those bodies.
In reality, the common person does not have a "soul" yet; they have the essence or seed of the soul, which must be grown through the "second birth." As Jesus explained, "With patience ye shall possess thy souls." (Luke 21) Thus, the development of the soul is the mere beginning of the path to full development. Afterward, there are far greater works to accomplish.
The term "soul" should not be confused with "spirit," which refers to a higher aspect of the Innermost (Atman; Chesed).