But He willed the Incarnation, which would not have been willed, had there been no original sin? So His Nature is not exactly the same as His will as you assert.
While I agree that there is a theological-philosophical problem with the Incarnation in regards to Original sin, it does not follow logically or necessarily from your argument, that because there is a problem, that therefore Gods “nature” is not the same as his “will”. The incarnation is a secondary issue that is dependent on Gods willing it, rather then a requirement or necessity. At the most this would present a challenge to the “Incarnation”–if not a refutation. However if you take on faith as I do, that God is “all-knowing”, then we must accept the proposition that Original Sin is in Gods “eternal knowledge”, and therefore it would be in Gods “perfect eternal will and love” to save humanity through the Incarnation.
On the other hand, I’m not quite sure that the Incarnation is wholly dependent on original sin; the unification of man and God through the incarnation may very well be apart of Gods eternal expression despite the chance that human beings may sin; and so the incarnation might have happened regardless; except, it would have been surrounded by different events (that’s just a personal theory of mine which is probably wrong). However, it’s more probable to be the case that the original sin and the incarnation where in some way destined to happen and cannot be removed from the events that occurred.
My arguments, concerning Gods attributes, are based on necessity. It’s what God has to be or would be if he was the Ultimate Cause of the Universe; that is the question. For example, if God is “Existence”, the Ultimate Being through which all existing entities have obtained “being”, then it is impossible that God cannot know all future events, since space/ energy and more importantly “Time”, requires “Existence” in order to “be” or “become”. Therefore there can be no future event that is not foreknown and not generated by God, since they are all subject to existence. What I mean by that is, from a “Gods Eye View” of things, all time is eternally one and present to God—there is no passing of time. In other words, time and the rest of the universe, from a “Gods eye view”, is a “static” “eternal” “extension” of Gods “creative”, “expression” and “Love”; even though from our point of view, from within the confines of time, there is a definite temporal beginning and a passing of one moment to the next.
How? Don’t ask me. It’s a matter of necessity because of the nature of the premise.
The point is, the unification of Gods will and nature is not a matter of opinion or argument; it is a necessary consequence of God’s Timeless attributes.