Here's a christological motto to live by: Nicea comes before Chalcedon.
What do I mean by this? I'm glad you asked.
It's common in christological debates to begin by thinking of the Council of Chalcedon, 451 AD (btw I'm not guaranteeing the quality/accuracy of the wikipedia links). There a two-nature christology was hammered out in which
We confess that one and the same Christ, Lord, and only-begotten Son, is to be acknowledged in two natures without confusion, change, division, or separation (ἀσυγχύτως, ἀτρέπτως, ἀδιαιρέτως, ἀχωρίστως; inconfuse, immutabiliter, indivise, inseparabilter).
And so, typically, thinking on the Person of Christ begins with a consideration of these two natures, humanity and divinity, which subsist in the one Person without confusion or change (upholding the integrity of Christ's genuine humanity and divinity) and without division or separation (upholding the unity of His humanity and divinity in one Person). Yet is this really where our thinking should begin?
Chalcedon is pretty universally regarded as a good ring-fence - defining the bounds of orthodox christology. But ring fences do not make good foundations!
So where should we begin? Well note that Nicea comes before Chalcedon. It was in 325 AD that the Council of Nicea considered the identity of Jesus of Nazareth. And crucially Nicea declared what the Scriptures clearly teach - that Jesus of Nazareth is 'of one being with the Father' (homoousios). Now here's the crucial thing - Nicea does not simply say 'the eternal Son' is 'of one being with the Father.' This is of course true, but Nicea says more than this. It is the Jesus who was born of the virgin Mary, who suffered under Pontius Pilate, who is declared homoousios with the Father.
Now why do I say that this was a necessary assertion from Nicea? Well, starkly put, who cares if the eternal Son is God if we can't say the same of Jesus of Nazareth! It's Jesus of Nazareth who says 'If you've seen me you've seen the Father.' (John 14:9) It's Jesus of Nazareth who says 'Son your sins are forgiven.' (Mark 2:5) It's the Man Jesus who lives our life and dies our death. If salvation is truly from the LORD then it has to be Jesus 'born of the virgin Mary and suffered under Pontius Pilate' who is declared fully God. Nicea necessarily and clearly does this.
And what does this mean? It means that before we've even gotten to Chalcedon we've affirmed that the Person of Jesus who is fully man and fully God exists entirely within the circle of divine fellowship which constitutes the being of God. Jesus the Man is of one being with the Father. If we could not affirm this then the revelation of Jesus would not be the revelation of God (contra John 14). If we could not affirm this then the salvation of Jesus would not be the salvation of God (contra Mark 2). But no, Jesus and the Father are one - not simply 'the Son' and the Father.
Why am I labouring this? Well I have a sneaking suspicion that the christology story most people have in mind is a little different. My fear is that people think the order of things goes something like:
1) we all know what divine nature is (some kind of essence probably!)
2) then (at Nicea) we insist that there is a trinity of Persons who we ought to confess as divine (and therefore in equal possession of this God-stuff)
3) then (at Chalcedon) we turn our attention to this pesky issue of how Jesus (who looks very different to our assumed conception of God-stuff ) is made up of God-stuff and man-stuff. And it's pretty freaky, and a mystery, but hey orthodoxy demands it so we'd better confess it.
It's caricature obviously but does that kinda vibe resonate with anyone else? It's a theological journey that treads this path:
Being of God (divine nature) => Trinity => Christ (two nature christology).
Or to put it even more crudely: "We all know God's essence is a load of 'omni's; then (weirdly enough) we affirm that these omnis are parcelled out equally among Three Persons and then (strangeness of all strangenesses) we declare that one of the Three not only has a God-nature (defined by these omnis) but also a man-nature (that's really very unlike His God-nature as defined by the omnis)." I confess that I have seen a lot of this kind of thinking in my own theology in the past. And it's pretty awful to be honest.
When we begin by looking through the wrong end of the telescope we are left looking at the human Jesus but this humanity is actually a problem - a barrier. True revelation of God lies behind the humanity (which is all we ever encounter of Christ) and so Jesus has actually concealed rather than revealed God.
But... Nicea comes before Chalcedon. This is not just true chronologically, it should also be true in our theological method. Nicea teaches us that our doctrine of the being of God; the trinity; and christology must be held together. These three concepts must mutually inform each other or else all three will be misconstrued. The Being of God is the relationship of the Three. And these Three are One not only as Father, Son and Spirit but equally (and crucially) as Father, Incarnate Son and Spirit. In this way divinity, trinity and christology are held together. Go here for another post of mine on Nicea.
The divine nature is precisely the communion of the Three - a communion that is in no way compromised by the incarnation. Jesus is fully God because He is the Son of the Father and the Anointed One with the Spirit. It is no wonder that He is so often identified as 'The Christ, the Son of God.' Christ's deity consists in these relationships and is never diminished by taking flesh. Thus His full humanity in no way contradicts His full deity. The Man Jesus exists fully and without remainder within the circle of divine life. Chalcedon upholds the full integrity of Christ's humanity, the complete perfection of His divinity, the absolute unity of His Person. What Chalcedon does not say, and what it must never be made to say, is that there is a humanity to Jesus that is beyond the divine homoousios. Nicea has for all time assured us that the Man Jesus is within the circle of triune fellowship which is the divine nature.
And this is the heart of our Christian hope. It means that the Christ I encounter in the gospel does reveal the very nature of God; He really is offering me the salvation of God and, through union with Christ, He really has brought me to participate in God's own life. (2 Peter 1:4). If we lose this, we lose everything.