The One Christ: St. Augustine's Theology of Deification
118 The Son's Descent dren of Adam have procured: corrupted human nature, sinful habits, and death.
This passage points to how the assumption of humanity is a necessary condition for the great exchange. God relies on our mortality because he, of course, by nature does not posses it. Christ establishes a unity between the immortal and the mortal in his very self, "later making us sharers in himself, but first becoming a participant in us. We had nothing of our own by which we could live, nor did he have anything from himself by which he could die. Therefore he struck a wonderful exchange with us by means of a mutual participation: ours was what allowed him to die, his is what allowed us to live."89 Augustine is careful not to verge on pantheism or to violate the divine nature in any way, as one of his most consistent pleas is to insist how divine interaction with creation changes only the created while divinity goes unaltered: "Because the Word was made flesh it was the very Word himself who was crucified, but the Word was not changed into humanity; rather, humanity was changed by its union with him. Human nature was changed in him to become nobler [melior] than it had been before, but it was not changed into the substance of the Word."90
The exchange is effected first by the Son's sharing in mortality and humanity's ascent is achieved not by anything of its own merit or power but through the graciousness manifest in this divine descent: "before we could become participants in his immortality, he had to become a participant in our mortality. But as he became mortal not because of anything in his own nature but by sharing in ours, so do we become immortal
89. s. 218C.1; Hill, Sermons (III/16), 194; adjusted; "participes sui postea facturus, quorum esset prior particeps factus. Nam nec unde uiueremus nos habebamus de nostro, nec unde moreretur ille de suo. Mirum proinde nobiscum egit mutua participatione commercium; nostrum erat, unde mortuus est; illius erit, unde uiuamus"; PLS 2.545–46.
90. en. Ps. 130.10; Boulding, Expositions (III/20), 148.