English for this rather old religious term is "hypostasis".
In this sentence it can be treated as ... this hypostasis of Christ...

See also (since it is related to Orthodox Chirch)
www.orthodoxunity.org/state01.html

Hypostasis of Christ
... Talk given at the SE Conference held in St. Augustine Fla. On Dec 10, 1999. Identifying the Antichrist. ...
localsonly.wilmington.net/jmalik/Hypostasis.html

Seee also : Christology Terms
... divinity of Christ. Thus the unity of Christ's hypostasis (person) does not imply any mixing of the divine nature and the human nature. prosopon (person, "mask ...
www.evergreen.loyola.edu/~fbauerschmidt/TH246_terms.html

... one hypostasis of our Lord Jesus Christ -- so that it means the union of many hypostases ... --->
www.iclnet.org/pub/resources/text/history/council.2constan....

Etc.
Yours,
Tagir.

'Aspect', I believe is the best match for the connotation of 'ипостась' generally associated with Jesus Christ. Depending on the context, however, 'quality' and 'attribute' may also be applicable.

Described in the Concise Oxford Dictionary as: in Christian theolog: a. the person of Christ, combining human and divine natures, and b. each of the three persons of the Trinity.

incarnation (cap.) = the union of divinity with humanity in Jesus Christ

I think gpritsker has it right, we are dealing with an attribute or quality. It just needs to be slightly more specific.


Justinian against Arianism:

"...divine nature is not changed into the human, nor the human into the divine; rather, whilst each remains within its bounds, the unity of personality (hypostatic unity) is produced by the Logos.

V. Lossky on the same subject:

"The dogmatic emphasis of the term Theotokos, as affirmed against the Nestorians, is above all Christological: what is defended against gainsayers of the divine maternity is the hypostatic unity of the Son of God become the Son of Man."

(Lossky, V., In the Image and Likeness of God, St. Vladimir's Seminary Press: 1974), pp. 195-210.