Here is something I posted elsewhere about the Incarnation:
Let "S" represent a human person:
1) S became a doctor
2) S became a Christian
3) S became a ruffian
In each of the cases listed above, it would be safe to conclude that some type of actual change or process has occurred to/regarding S. But if we now consider another proposition:
4) The Logos became flesh
We are asked to believe (by the majority of Incarnation advocates) that change neither occurred to the nature of the Logos nor to the divine person who was supposed to be the subject of the Incarnation: no real alteration took place. Yet if the Logos became (was made) flesh, it is still hard to comprehend how he (the person) became flesh without undergoing some kind of change. To just argue that God cannot experience actual change, the Logos is God, therefore, the Logos did not experience actual change seems like petitio principii to me.
Using the language of assumption doesn't make the problem go away either. If by assume, we mean "take to oneself" (Aquinas in the Summa Theologica), then to say that the Logos assumed human nature (flesh) could possibly be akin to assuming another identity or assuming a posture that one did not previously had. No, I'm not saying that Christ just assumed a new identity; my point is that the word "assumption" could also indicate change/alteration.
Before: The Logos is strictly spirit
Post-Incarnation: The Logos is flesh
However, most say that no actual change occurred to the nature or person of the Logos (Word).