What does Paul mean in Ephesians 3:19 when he says “that you may be filled with all the fullness of God?” Girolamo Zanchi, in his Commentary on Ephesians, interprets Paul to mean that believers are partakers of the divine nature, a participation which depends upon one understanding “the mysteries of piety and its causes, that is, by understanding the love of God in Christ toward us.” This is not a bare cognitive assent, however, but is combined with an experience [sentio] of the love of God within one’s “inner man” by means of grace. Zanchi, like Aquinas, considers union with God to occur primarily through a certain created likeness of God within the soul, or in other words, a renewal of the image of God in the soul by means of certain infused qualities (i.e., wisdom, righteousness, etc.). He explains what it means to be “filled with the fulness of God”:
Translation: Girolamo Zanchi on Ephesians 3:19
By what, then, do we become strong? By a power and virtue, not human, but divine. So, [Paul] says, “that you may be strengthened with power, that is, of God.” Therefore, all of the virtues are excited within us, they stand upright, and are nourished by the power [δυνάμει] and virtue of God, and these are really nothing other than a certain divine power created, excited, and inflamed through the Holy Spirit within us, by which [we are] good, strong, wise, righteous, and finally, we are such as God wants us to be, and by which we have the ability, whatever ability we have, [to be] good. This is the power [δυνάμιν] of God that Peter calls the divine nature: “That you may become (Peter says) partakers of the divine nature.” By the word “nature” here [Peter] means a created quality by which we become like God. Paul calls [it] grace: “By the grace of God I am what I am & his Grace in me was not vain” (1 Cor. 15).
Zanchi, In d. Pauli epistolam ad Ephesios Commentarius, 1594, p. 201.