Martin Luther was a "theologian of the cross", whereas medieval scholastics were in his view, "theologians of glory." That is, many theologians considered God in himself in ways that did not begin with the "alien" (his incomprehensible) work of Christ in his humanity and upon the cross. There is a cradle and a cross to be understood before we can see the glory of God.
Carl Trueman explains this further...
"The theology of the cross is more than just a way of looking at God, however. For Luther, it brings to the fore both the depth of God’s love for sinful humanity, that God himself was willing to undergo such suffering, weakness and humiliation on behalf of helpless sinners, and also underlines that suffering and weakness is a central part of the Christian’s strength experience here on earth. In Christ, God has so identified himself with humanity as to become one with fellow humans. He has endured not only the mundane inconveniences of our existence but has even suffered in a supreme sense on our behalf, that suffering which is captured in a deep and inexplicable way in the cry of dereliction on the cross. These are, of course, deep theological waters, but for Luther the crucial dimension of God’s saving power was precisely this profound humiliation of himself in human weakness. He had a saying: Don’t give me God without giving me his humanity. The point was simple: it is in the incarnation, in the flesh of Christ, that God both is, and shows himself to be, gracious towards us. Luther rejoiced in the fact that he did not worship a God who was far way, a despot, an abstract and anonymous philosophical principle. No—he worshiped a God who had come close, so close that he even clothed himself in human flesh; a God who was so merciful that he was prepared to welcome sinners into his presence as if they had never sinned; a God who was so loving that he happily freed men and women from all manner of physical and spiritual bondage so that they might know true life; and a God who was so strong that he was prepared to make himself nothing and die that terrible death on the cross in order that human beings should never have to die.
"At the centre of Luther’s doctrine of God, then, stands the humanity of Christ, for it is there that God is merciful and gracious.
"One does not become a theologian by knowing a lot about God; one becomes a theologian by suffering the torments and feeling the weakness which union with Christ must inevitably bring in its wake.
"‘Why me? Why is this terrible thing happening to me? I’ve done nothing wrong.’ For Luther, the question must be answered by looking to the cross: if suffering, persecution, injustice, hatred and scorn are the lot of Christ, and if it is through these very means that God, in a manner incomprehensible and unexpected, achieves his goal of saving helpless sinners, then are we to expect our lot to be any better?
"God always achieves his proper work in us (i.e. our salvation) through his alien work (our suffering and weakness)."
~ Carl Trueman, Reformation:Yesterday, Today & Tomorrow (Christian Focus, 2011 reprint)