The term is relatively common in classical texts, and has the meaning of "union" or "unity".
Process of unification
Henosis, or primordial unity, is rational and deterministic, emanating from indeterminism an uncaused cause. Each individual as a microcosm reflects the gradual ordering of the universe referred to as the macrocosm. In mimicking the demiurge, one unites with The One or Monad. Thus the process of unification, of "The Being" and "The One," is called henosis, the culmination of which is deification.
Henosis for Plotinus was defined in his works as a reversing of the ontological process of consciousness via meditation toward no thought and no division within the individual. As is specified in the writings of Plotinus on Henology, one can reach a tabula rasa, a blank state where the individual may grasp or merge with The One. This absolute simplicity means that the nous or the person is then dissolved, completely absorbed back into the Monad. Within the Enneads of Plotinus the Monad can be referred to as the Good above the demiurge. The Monad or dunamis is of one singular expression, all is contained in the Monad and the Monad is all. All division is reconciled in the one, the final stage before reaching singularity, what is called duality is completely reconciled in the Monad, Source or One. As the one, source or substance of all things the Monad is all encompassing. As infinite and indeterminate all is reconciled in the dunamis or one. It is the demiurge or second emanation that is the nous in Plotinus. It is the demiurge or nous that "perceives" and therefore causes the force to manifest as energy, or the dyad called the material world. Nous as being, being and perception manifest what is called soul. Plotinus words his teachings to reconcile not only Plato with Aristotle but also various World religions that he had personal contact with during his various travels. Plotinus' works have an ascetic character in that they reject matter as an illusion. Matter was strictly treated as immanent, with matter as essential to its being, having no true or transcendential character or essence, substance or ousia. This approach is called philosophical Idealism.
Within the works of Iamblichus of Chalcis, The One and reconciliation of division can be obtained through the process of theurgy. By mimicking the demiurge, the individual is returned to the cosmos to implement the will of the divine mind. One goes through a series of theurgy or rituals that unites the initiate to the Monad. These rituals mimic the ordering of the chaos of the Universe into the material world or cosmos. They also mimic the actions of the demiurge as the creator of the material world. Iamblichus used the rituals of the mystery religions to perform rituals on the individual to unite their outer and inner person. Thus one without conflict internal or external is united and is The One.
In Eastern Orthodox Christianity, but also in western mysticism, henosis can be acquired by theoria, hesychasm and contemplative prayer. Yet, the concept of theosis, or deification, differs from henosis, since created beings cannot become God in His transcendent essence, or ousia but only by sharing His love's strength, that is to say a participation of the life of God.
