For if he has brought to completion his mystical work of becoming human, having become like us in every way save without sin (cf Heb 4: 15), and even descended into the lower regions of the earth where the tyranny of sin compelled humanity, then God will also completely fulfill the goal of his mystical work of deifying humanity in every respect, of course, short of an identity of essence with God; and he will assimilate humanity to himself and elevate us to a position above all the heavens. It is to this exalted position that the natural magnitude of God’s grace summons lowly humanity, out of a goodness that is infinite. The great Apostle is mystically teaching us about this when he says that in the ages to come the immeasurable riches of his goodness will be shown to us (Eph 2: 7).
We too should therefore divide the “ages” conceptually, and distinguish between those intended for the mystery of the divine incarnation and those intended for the grace of human deification, and we shall discover that the former have already reached their proper end while the latter have not yet arrived. In short, the former have to do with God’s descent to human beings, while the latter have to do with humanity’s ascent to God.
…Existing here and now, we arrive at the end of the ages as active agents and reach the end of the exertion of our power and activity. But in the ages to come we shall undergo by grace the transformation unto deification and no longer be active but passive; and for this reason we shall not cease from being deified.
From “Ad Thalassium, On Jesus Christ and the End of the Ages” by Maximus the Confessor.