IAO is first mentioned in the Pistis Sophia: The Gnostic Tradition of Mary Magdalene, Jesus, and His Disciples. It is a mantra very rich in symbolic meaning, and like most Gnostic texts a bit mysterious in origin. Among Gnostics it seemed to take not only the form of a mantra but also almost a shorthand version of the name of God also similar to the tetragrammaton which was the name of the biblical god. The text within the Pistis Sophia that mentions IAO reads as such:
And Jesus made invocation, turning himself towards the four corners of the world with his disciples, who were all clad in linen garments, and saying: “iaō iaō iaō.” This interpretation: iōta, because the universe hath gone forth; alpha, because it will turn itself back again; ōmega, because the completion of all the completeness will take place.
~ Pistis Sophia, translated by G.R.S. Mead
This is quite interesting to me because in this progression from iōta, to alpha, to ōmega is a bit at odds with the traditional biblical text that speaks of god as being the alpha and the ōmega; the implication that god is both the beginning and the ending of the All. The addition of Iōta hints towards a hidden aspect of God (take note of the capitalization I am using, because it is quite intentional here). The Gnostics had some interesting thoughts on the nature of the god of the Pentateuch. And I believe this is key to understanding their writings. A key to deciphering their esoteric writings is knowing how they felt about Yawheh (or Jehovah). They had a name for this deity or god (lowercase “g”), being Yaldabaoth, who was not the benevolent force that modern Judaism and Christianity takes as a given. But perhaps I should get back on topic here.
IAO also has by some interpretations Egyptian roots in its meaning. The iōta standing for Isis, no not the terrorist organization; I particularly hate that that acronym has been attributed to them. She was quite the motherly figure and wife of Osiris. The alpha representing Apophis who represented the powers of destruction and death. He was the arch nemesis of the Sun/Son god Ra. And Osiris as ōmega, who is a great symbol of rebirth, almost a parallel of Jesus in a sense in that he was slain and raised from the dead, except in his case by his wife Isis.
Overall the formulation of IAO represents an archetypal story of the creation, destruction, and rebirth or reincarnation, if you will, of the human soul. It is a timeless symbol with much meaning and psychological strength behind it. This could also represent an alchemical transmutation of one state of mind or situation into another. Either way, it is a powerful tool for those with eyes to see and ears to hear. I’ll leave you with a decent chant that perhaps you can use in your own meditation purposes. Peace and blessings to all.