So, what does Christocentric anthropology look like?
First of all, it begins with Jesus, and asks the question: what does it mean to be Jesus? Because if Jesus is 'the Man', the only real human being, humanity cannot be discovered apart from him. Of course, there are many ways we could look at Jesus, and many perspectives from which we could view him. When it comes to anthropology, we must consider Jesus the Man (albeit the Man who is God). There are two essential things to consider about this Man - two relationships. On the vertical axis, Jesus is man for God. This captures a number of different things. Jesus, considered as a human being, is God's creature; his human nature has no existence except that which is granted to it in the incarnation through its union with the Logos. The sense in which Jesus is man for God goes beyond this, however, to embrace his responsibility. Everything that is not God exists for God in some way, but Jesus exists for God as an active, responsible being. He exists to willingly fulfil the will of God. Meanwhile, on the horizontal axis, Jesus is man for man. At the surface level, this expresses the fact that Jesus comes to do humanity good. At a deeper level, the man Jesus would not exist except as he comes to do man good. Being 'for man' is not something that is incidental to Jesus; it defines his being as the incarnate Son of God. And then again, Jesus is 'for man' because in his life, death, and resurrection he takes the place and takes up the cause of the human race and each member of it.
To be Jesus is to be man for God, and man for man.
But secondly Christocentric anthropology recognises that Christology and anthropology are different things. We cannot read a general doctrine of humanity from the being of Jesus. He is the God-man, unique and above us in every way. Barth doesn't put it like this, but I suppose you could say we should not be Christomonist when thinking about humanity, but genuinely Christocentric. Jesus is the centre point of humanity, and general humanity stands around him; Christology is the centre and anthropology is the periphery. Nevertheless, we can move from the centre to the periphery. Humanity cannot be Jesus, but it must correspond to Jesus.
Jesus is man for God - uniquely so, through the incarnation. But corresponding to this is the determination of man generally as one who belongs to God and responds to God. This vertical relationship exists, whether the individual human being acknowledges it or seeks to efface it. The relationship holds because, in the faith of human unfaithfulness, and indeed the impossible yet frequently made decision for inhumanity on the part of individual human beings, God is faithful. Human beings cannot unmake themselves, or make themselves something other than what they are.
Jesus is man for man - uniquely so, through his representative and substitutionary role. But corresponding to this is the determination of man generally as one who stands with other men. No definition of humanity which makes the individual prior can possibly be correct. To be man, says Barth, is to be fellow-man, to stand in an I-Thou relationship with other human beings. Again, this must be so. We do stand in relationship to others, whether we like it or not. We cannot, and should not, stand in their place as Jesus does, but we should stand alongside. We exist to help one another. This being as fellow-man is shown most clearly in the existence of humanity as male and female, man and woman. "It is not good for the man to be alone".
These conclusions - that man is for God, and with other men - could be reached in other ways. But only from Jesus can they be shown to be certain and absolutely determinative for human existence.