It is interesting that Atman in ancient India was understood absolutely not like we understand the Soul.
The microcosm (man) mirrors the macrocosm (the universe). Both have an essence, a true nature, a ‘self ’ (atman), which is the same for both. So at the cosmic level brahman and atman are to be understood as synonyms. Being an essence, that atman is unchanging: it is being as opposed to becoming. Being is also a plenum, since it can be predicated of everything that exists. Unhappiness is always due to a lack of something; being, a plenum, can lack nothing; therefore being has no unhappiness, but is bliss.
R. Gombrich “How Buddhism Began”