Celebrating the Saints for the memorial of St Athanasius is an excerpt from his De Incarnatione:
The Word of God, incorporeal, incorruptible, and immaterial, entered our world ...In the loving kindness of God the Word came to us, and was revealed among us openly.
These words give us some idea of how Athanasius' confession of the reality and fullness of the Incarnation stands at the heart, the centre of the Church's mission. Our Christological centre, in other words, defines and gives meaning to the Church's mission: without this Christological centre, our mission begins to disintegrate. It is because the God who is "incorporeal, incorruptible, and immaterial, entered our world", that the Church evangelises. The imperative to evangelise lessens when the Word is deemed to be homoiousios rather than homoousios - because then God's gracious commitment to this world is lessened. Then it was not the One who is fully and truly God who "entered our world ... and was revealed among us openly".
But the Word is homoousios. And the Church's mission, of course, is shaped by the missio Dei. God fully and truly entered this world for the world's salvation. From this Christological centre flows the Church's mission in the world.
++Rowan puts it this way:
The phrase in the Creed, 'being of one substance with the Father' or 'of one being with the Father, can sound a bit chilly and technical - even worse in the form 'consubstantial' ... Yet it ought to be one of the most exciting words in our vocabulary, telling us that what is happening in the person and activity of Jesus of Nazareth, the workman from the backwater town, is one with the essence of God and nothing less.
Benedict similarly points to the significance of Athanasius' theology:
The fundamental idea of Athanasius' entire theological battle was precisely that God is accessible. He is not a secondary God; he is the true God, and it is through our communion with Christ that we can truly be united to God. He has really become 'God-with-us'.
The Church proclaims God to the world, because God - not one 'similar' to God - entered the world for the world. In his introduction to a 1944 edition of De Incarnatione, C.S. Lewis provocatively suggested that Arian Christianity was "one of those 'sensible' synthetic religions which are so strongly recommended today and which, then as now, included among their devotees many highly cultivated clergyman". The specialists on Arius might recoil at Lewis' language, but surely he was (again) onto something. If the One who entered this world was not fully and truly God, there are weighty ramifications for the Church's mission. If God found this world too distasteful to fully and truly embrace, so will the Church.
The heart of our mission is the Christological centre. It is, then, entirely appropriate that De Incarnatione should commence with a declaration of the evangelical nature of the scandal of the Incarnation:
Thus by what seems His utter poverty and weakness on the cross He overturns the pomp and parade of idols, and quietly and hiddenly wins over the mockers and unbelievers to recognise Him as God.