The quote from Philipians 2:5-6 given by our Mormon friend must be read and understood in light of the incarnation, whereby we do say that it is not robbery that He be considered equal with God the Father (as He truly is, being of one essence with God the Father and with the Holy Spirit in the uncreated and undivided Holy Trinity), which further underlines the amazing reality of the incarnation, about which we say things like the following (from the Nativity liturgy of the Coptic Orthodox Church):
"O Thou, THE BEING throughout all time, have come to us on Earth / You have come into the womb of the virgin / You the infinite, You the infinite, being God, did not consider equality with God a thing to be held onto / but released it and emptied Yourself / and took the form of a servant / and blessed my nature in Yourself / and fulfilled Your law on my behalf / You have shown me the rising up from my fall / You have given release to those who were bound in Hades / You have lifted the curse of the law / You have abolished sin in the flesh / You have shown me the power of Your authority / You gave sight to the blind / You raised the dead from the tombs / You established nature by the word ..."
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The connection between the quoted portion of the prayer and the quoted portion of the scriptures should be clear: Our Lord Jesus Christ, being God in all ways and from all time, did not consider His equality a thing to be held on to to the exception of coming to us in the form of a servant, which He did by His incarnation and birth from the holy Theotokos St. Mary, blessing and sanctifying our nature in the process just as He has redeemed all mankind and the entire creation by His life, preaching, crucifixion, death, and resurrection.
This is an entirely different message and understanding than the very strange "He has to have
this type of body or else they're not equal" idea that we are getting from our Mormon friend, which seems to be based on what would best serve Mormon philosophy rather than saying anything about the
nature of God. Perhaps it is yelling once again into the void, but I feel it appropriate here to reiterate that the equality of the Persons of the Holy Trinity is precisely in this
equality of their nature -- that they are of one and the same nature (or essence, or substance -- these are synonyms): the divine nature. It is in no way a statement of form, but of nature.
(This is why when Mormons keep saying "They can't be the same substance if they don't both have bodies", it elicits an immediate no. Saying such things knows that you are not understanding the basics of Christian theology, but instead substituting your Mormon theology whenever you run up against something you don't understand, rather than accepting what you are given by people who actually do use this terminology.)