This is Eberhard Busch quoting and summing up parts of Karl Barth's Doctrine of Reconciliation. I think this is hugely important stuff -- such that I hesitate to spoil it with introductory comments. So give it a read and I'll spoil it with follow-up comments instead:
"'Reconciliation . . . is the fulfillment of the covenant between God and man' . . . .
Barth’s understanding of the covenant has an unusual emphasis at this point when he says that God involves himself with humans despite sin. . . . if it were otherwise, God’s relationship to human beings would be dependent upon sin. Sin would either be immortalized or God would have nothing to do with humans apart from sin. As God’s reconciling reaction to sin takes place in the act of his [pre-existent] covenant will, it cannot thus be pulled into the undertow of sin.
For God, this can only mean allying himself with human beings notwithstanding their sin. According to Barth, the reconciliation that takes place in the fulfillment of God’s covenant has the character of an effective protest. Barth even speaks (and here he uses the concept in a different way than usual) of the character of judgment. Because it takes place as a reaction to sin in God’s covenant action, his judgment is the fulfillment of God’s faithfulness as he rejects Israel’s unfaithfulness . . . .
That reconciliation took place within the covenant means ‘with divine necessity’ that the Word became flesh, yet ‘not simply any flesh, any man humbled and suffering. It became Jewish flesh. The church’s whole doctrine of the incarnation and the atonement becomes abstract and valueless and meaningless to the extent that this comes to be regarded as something accidental and incidental.’"
(Quoted from Eberhard Busch, Barth, 2008, pages 42-43; referring to Barth excerpts from Church Dogmatics IV/1- 22, 34, 71-3,181-4)