God’s divinity rightly understood includes his humanity. Where do we learn this? How is this statement justified and what indeed demands it? It is a Christological statement, or rather a statement based on and to be developed out of Christology. … One thing is certain, that in Jesus Christ, as we know him from the witness of Holy Scripture, we have not to do with humanity in the abstract… Nor, on the other hand, with God in the abstract… In Jesus Christ there is no barrier on the human side upwards nor one on God’s side downwards. Rather, what we have in him is the history, the dialogue, in which God and humanity meet and are together, the reality of the covenant concluded, kept and completed by them mutually. In his one person Jesus Christ is at once as true God humanity’s faithful partner, and as true human being God’s faithful partner, both the Lord abased to community with humanity, and the servant exalted to community with God, both as the Word spoken from out of the highest, most glorious Beyond, and the Word heard in the deepest, darkest Here and Now: both unconfined, but also undivided, wholly the One and wholly the Other. Thus, in this unity Jesus Christ is the Mediator, the Reconciler between God and humanity. Thus, demanding and awakening faith, love and hope, he acts for God before humanity – and, representing, atoning, interceding, for humanity before God. Thus he attests and guarantees to God free human gratitude. Thus he establishes in his person God’s right vis-a-vis his humanity, but also humanity’s right before God. Thus he is in his person the covenant in its fullness, the close at hand Kingdom of Heaven, in which God speaks and humanity hears, God gives and humanity receives, God commands and humanity obeys. God’s glory shines in the highest – but also from the highest into the depths – and peace on earth eventuates among the people of his good pleasure. And just in this way, as this mediator and reconciler between God and humanity, Jesus Christ is for both revealer. Who and what God is in truth, and who and what humanity, we have not to explore and construct by roving freely far and near, but to read it where the truth about both dwells, in the fullness of their union, their covenant, that fullness which manifests itself in Jesus Christ.
Karl Barth, The Humanity of God, (1956) quoted in ‘Selected Writings of Karl Barth: Theologian of Freedom’, ed. Clifford Green, 1989, p.52-53.