From Oswald Bayer’s interpretation of Martin Luther’s Theology, pages 228-9:

“The effect that the law creates is not surprising. One has no trouble understanding what it means to rely on oneself and on one’s own deeds; the action-consequences relationship has its own logic. But the gospel is absolutely, completely incomprehensible. That God rescues one from, and brings one safely through, the deserved judgment is a miracle. Law and gospel cannot be plausibly intertwined together; their existence is hard and fast in opposition to each other. The gospel is literally a paradox: it stands against that which the sinner can reasonably expect; it stands against damnation.

It is thus not surprising that the communion between the sinning human being and the God who justifies through Jesus Christ by the Holy Spirit is incomprehensible; it is stupefying – astonishing – which does not lead one to be calm and at peace. Rather, it is described by Luther as a ‘stupendumduellum – as a  duel that arouses astonishment, as a duel like the one Jacob engaged in at Jabbok (Gen. 32). That this deadly confrontation between God and humanity is a ‘happy exchange,’ is a miracle. The one who has escaped from judgment and death cannot be sufficiently astounded about this.

‘The love of God does not find one worthy of its love to be present already, but [first] creates it.’ In this sense God is ‘God and no mortal’ (Hos. 11:9). For: ‘human love comes for the one who holds another worthy of love [already].’ (Luther, WA 1:354.35f). By contrast, the justification of the ungodly  (Rom 4:5) is nothing less than the resurrection of the dead and the creation out of nothing (4:17).”