God, you see, wants to make you a god; not by nature, of course, like the One whom He begot; but by His gift and by adoption (Augustine of Hippo, Serm. 166.4).
There are two kinds of deification. The first kind refers to the “elevation of man to the highest level of his natural powers . . . [by] the divine power of grace [being] active in him . . . [The second kind of deification refers to that] progress which man makes beyond the limits of his natural powers, beyond the boundaries of his nature, to the divine and supernatural level” (D. Staniloae, 2002, p. 363). To pass from the first kind of deification, that which we hear about on a daily basis, to the second kind, that is the deification which we rarely hear about because it has become all but extinct in Western Christianity, a leap of grace occurs through the goodness of God the Father, because “man too works during the first stage, but during the second, only God” (ibid.).
“The union to which we are called is neither hypostatic as in the case of the human nature of Christ, nor substantial as in that of the three divine Persons. Rather it is a union with God in His/Her energies, or union by grace making us participate in the divine nature, without our essence becoming thereby the essence of God” (Aleaz, 2000).