Theosis comes from the Greek θέωσις and literally means “divine state” — Theo (God, divinity) + osis (state or condition). Think of words like theology (God-talk) and gnosis (a state of knowledge) to understand how the word is constructed.
Theosis
Three Dimensions of the Contemplative Life
The “idea” that I’m referring to is the notion that Christian spirituality can be understood as involving three stages. To give this notion a bit of gravitas, Origen appealed to the Hebrew Scriptures.