The Muslims are right: Jesus was just a man. He wasn’t God. He was just a dude. He had a single nature and that nature was human. In fact, Jesus was peccable, which is to say he was able to sin. Adds a whole new dimension to the temptation in the wilderness story doesn’t it? Our saviour really could have failed, he really could have given in to the temptations!
However, at no point did he actually sin. If we conceive of sins as the bricks in a wall that stands between us and God and separate us from him, then consider what it means for Jesus to not have to contend with such a barrier. At all times, Jesus the man had full and direct access to God. There was no sin that stood in his way. In other words, from the moment of his conception all the way through his life and ministry, and even up to his death; Jesus experienced a profound unity with God and a full theosis.
Now, Jesus was fully man, which means that he inherited a fallen, imperfect human nature just like the rest of us. And this was why he needed to be baptised! Baptism removes the curse of original sin, which Jesus suffered from just like all of us, even if he never commit any actual moral fault.
But Jesus experienced full theosis, which is to say that even though he was merely a man by nature, it would be accurate to call him “fully God” by participation. And this would hold true for the duration of his entire life. So there is a sort of dyophysis at play: Jesus is fully man by nature, and fully God by participation, and there is a strict separation between the two natures. If at any time he had slipped up and sinned, he would have lost his full participation in divinity, as the bricks in the wall between him and God would have begun to stack up.
But no, Jesus was fully united to the divine λογος for his entire life. Never did he slip up. There have been many saints, Christian and otherwise who have also achieved a full unity with the λογος, for example Muhammad and Buddha, but what separates these saints and mystics from Jesus is that they begun their journey behind the wall of sin, and had to dismantle it brick by brick, whereas Jesus experienced theosis for the entire duration of his life.
Now, Jesus died. For the purposes of this discussion the details are not relevant, whether it was by murder or by old age does not matter. The crucial point is that this innocent man died; the only man who had ever lived his entire life without sinning once. But the wages of sin is death, so how could a man who had never sinned be subject to the penalty of death? And so the Justice of God becomes manifest as God raises Jesus from death to new life; a new life from which he will never die again.
But something funny happened as Jesus passed from death to new life. His nature changed. He took on an eschatalogical existence. No longer was he a dyophysis of created nature and divine participation. Instead he takes on the divine simplicity of a miaphysis; he becomes God! My thesis is therefore that the full incarnation did not occur at Christmas, but at Easter. Jesus was not born as God, he became God. Yes there was a sense in which he was fully God for his entire life and ministry, but this was merely by “participation”, not by “nature”. However the game changed after the resurrection. Jesus truly could be referred to as fully God in every respect. In fact, all of the imperfections and limitations of his human nature were swallowed up in the divine nature, like a drop in the ocean. Nevertheless he retained his created attributes.
This is why it is now appropriate to worship Jesus as the one true God. He has attained the divine perfections and exists already at the end of history, in the eschaton. This is why he says “no one comes to the father except through me”. God is eternally hidden, unmanifest, and there is valid no way to worship him, despite his being the only valid object of worship. But Jesus changes all that. He has broken the curtain that separates us from God in half and taken on a tangible form. Now we direct our worship towards this man Jesus, in the Eucharist, in the flesh. He became God, but by being God, he always was God. And so it will be with us. All of us will achieve theosis, and then all of us will achieve resurrection, and finally all of us will become the λογος incarnate. But while we are pilgrims here, on this side of the eschaton, waiting for that glorious resurrection, only Jesus is God, and only him do we worship.