The Self-Donation of God, chapter 9:
"The genus majestaticum posits that Christ's humanity possesses by communication the fullness of divine attributes when considered in the abstract. Chemnitz describes the genus thus: “so that when we speak of these matters in the schools we can be correct not only in calling Christ a man or saying that the Son of Man makes alive, but also we can then rightly speak in the abstract or in abstract language of the assumed nature as being united with the Logos. We can say that the flesh of Christ, which is united with the Logos, makes alive and that the blood of Christ cleanses from sin.” Vainio comments: “[t]he third genus . . . refers to the supernatural gifts and attributes Christ’s human nature receives in the hypostatic union. Since God’s attributes and essence are inseparable, these supernatural gifts and attributes are God’s essence.”
Gerhard observes that there was a difference between Lutheran theologians of the second generation as to whether one should speak of the glory of God communicated to Christ's human nature in the abstract. Some thought it was proper (notably Chemnitz and Johannes Brenz) others did not (notably Tileman Heshusius). Gerhard comments that this was ultimately a logomachy and not based on any substantive disagreement about the genus. Some claimed that considering the human nature in the abstract entailed thinking of only the essential attributes of his humanity. Therefore, since it was improper to say that divine attributes had been communicated to the human essence (this would entail the heresy of Eutyches, condemned by the fourth ecumenical council), it was not permissible to say that such glory had been communicated to the human nature in the abstract. Others disagreed and stated when a person considers the human nature of Christ in the abstract one must always think about it as it exists in the context of the hypostatic union. To be more exact, because the human nature is anhypostasis, it has never existed and never will exist, except in the concrete unity of the person of the Logos. It therefore follows that it must always be thought of as possessing the fullness of divine glory, because even when considered in the abstract the human nature was still the human nature of the Logos. This latter answer seems more satisfactory for of number reasons. First, terminologically speaking, it creates space for a clearer linguistic distinction between the genus majestaticum and the genus idiomaticum. Secondly, as we shall see below, it more closely replicates the Bible’s own manner of speaking about Jesus. This being said, it should be observed that the other position is technically speaking not incorrect, simply less terminologically precise.
In insisting on the full communication of glory to Christ's humanity, it should be observed that Chemnitz is not positing transmuting of humanity into divinity. Throughout the sixteenth and seventeenth centuries (as it is at present in many circles) this was a common charge of those among the Reformed communions who rejected this genus. As we noted earlier, both Calvin and Zwingli claimed that there was no communication of glory to Christ’s humanity and therefore his body was confined to heaven. From their perspective, since Lutherans believed that Christ’s possessed the fullness of divine glory and could exercise that glory by being present in many places at once (most notably in the Lord’s Supper) they must logically believe in the transmutation of Christ’s humanity into his divinity. Working from Chemnitz’s definitions, it is easy to observe that this charge is utterly without merit. The Lutheran claim is not the human essence is somehow mixed with the divine nature. Rather, the human possesses divine glory by communication within the personal union brought about by the Incarnation."