I am preparing now to give a presentation at the Antiochian Orthodox Institute in the Fall on the topic of divinization or theosis according to St. Isaac the Syrian. I have been enjoying reading through the latest edition of St. Isaac’s homilies, and when I was asked to present a small lecture on some aspect of the topic of theosis, I suggested that my focus be St. Isaac. Most of the time, when Orthodox Christian people speak about theosis, they focus on the language and patterns presented in the Philokalia. Specifically, following St. Maximus the Confessor, we usually speak of three steps or phases in the process of theosis. [By the way, theosis–also sometimes called deification or divinization–refers to the process or experience by which one becomes, by Grace, more like Christ, that is more like God]. The three steps or stages of theosis according to St. Maximus the Confessor and the tradition of the Philokalia are these: purification, illumination and theosis.
In this most common way to look at or present the process or experience of theosis, purification generally refers to our cooperation with the Grace of God to purge passionate thoughts from our minds. But purifying our minds of passionate thoughts begins with controlling our bodies through ascetic discipline. Therefore, the beginning of theosis is often found in beginning to control oneself physically leading to a knowledge of oneself that makes the purification of the thoughts, by the Grace of God, possible.
Illumination refers to the knowledge of God, again and always granted by Grace, that transcends the rational aspect of our minds. This knowledge of God is often referred to as noetic after the Greek word for ‘mind’; however, in this context it does not refer to ‘mind’ as we usually think of the word in English. It refers to the aspect of our mind that is open to and perceives spiritual, heavenly realities. There is no equivalent word for this aspect of the mind in English, which is why the Greek word noetic is generally used, although the words ‘heart’ and ‘spirit’ are sometimes used in English to try to get at this higher or deeper knowledge: for example, we might say something like “knowing God in your heart” or “to know God spiritually” to try to distinguish this kind of knowledge from merely rational knowledge, knowledgeabout God.