More from Carl Trueman’s article Luther’s Theology of the Cross:
This insight is one of the factors in Luther’s thinking that gives his theology an inner logic and coherence. Take, for example, his understanding of justification, whereby God declares the believer to be righteous in his sight, not by virtue of any intrinsic righteousness (anything that the believer has done or acquired), but on the basis of an alien righteousness, the righteousness of Christ that remains external to the believer. Is this not typical of the strange but wonderful logic of the God of the cross? The person who is really unrighteous, really mired in sin, is actually declared by God to be pure and righteous! Such a truth is incomprehensible to human logic, but makes perfect sense in light of the logic of the cross.And what of the idea of a God who comes down and loves the unlovely and the unrighteous before the objects of his love have any inclination to love him or do good? Such is incomprehensible to the theologians of glory, who assume that God is like them, like other human beings, and thus only responds to those who are intrinsically attractive or good, or who first earn his favor in some way. But the cross shows that God is not like that: against every assumption that human beings might make about who God is and how he acts, he requires no prior loveliness in the objects of his love; rather, his prior love creates that loveliness without laying down preconditions. Such a God is revealed with amazing and unexpected tenderness and beauty in the ugly and violent drama of the cross.