This supernatural order is denominated the order of regeneration and grace. It is cognate with the order of the hypostatic union, but not identical with it. The personality of the divine Word is communicated only to the individual human nature of Jesus Christ, who is not only the first-born but the only-begotten Son of God. God is incarnate in Christ alone. The union of his created substance with the divine substance, without any permixture or confusion, in one person, is something inscrutable to reason. The knowledge, sanctity, beatitude, and glory of his human nature are effects of this union, but are not it. These effects, which are due to the humanity of Christ as being the nature of a divine person, and are its rightful and necessary prerogatives, are communicable, as a matter of grace, to other individuals, personally distinct from Christ. {151} That is to say, sanctity, beatitude, and glory do not require as the necessary condition of their community ability the communication of a divine personality, but are compatible with the existence of an indefinite number of distinct, finite personalities. All those rational creatures, however, who are the subjects of this communicated grace, are thereby assimilated to the Son of God, and made partakers of an adopted sonship. This adoptive sonship is an inchoate and imperfect state of co-filiation with the Son of God, which is completed and made perfect in the hypostatic union. The order of grace, therefore, though capable of subsisting without the incarnation, and not depending on it as a physical cause, can only subsist as an imperfect order, and cannot have in itself a metaphysical finality. The incarnation being absent, the universe does not attain an end metaphysically final, or actualise the perfection of the ideal archetype. The highest mode of the communication of the good of being, the most perfect reproduction of the operation of God _ad intra_, in his operation _ad extra_, which the Father contemplates in the Word as possible, remains unfulfilled. Those who hold, therefore, that the incarnation was not included in the original creative decree of God must maintain that in that decree God did not contemplate an end in creating metaphysically final. They are obliged to suppose another decree logically subsequent to the first, by virtue of which the universe is brought to an metaphysically final in order to repair the partial failure of the angelic nature and the total failure of human nature to attain the inferior, prefixed end of the first decree. Nevertheless, decrees of God are eternal, God always had in view, even on this hypothesis, the incarnation as the completion of his creative act; and only took the be occasion which the failure of his first plan through sin presented to introduce one more perfect. Billuart, therefore, as the interpreter of the Thomist school, maintains that God revealed the incarnation to Adam before his