Knowing God, it is what we as Christians all desire; we want to not only know Him, but know that we have a more sure way of knowing God. In the history of the church and ideas there have been multiple ways to try and tackle this. There have been mystical (Platonic) types of attempts at this; there have been chain-of-being attempts at this (Thomism) wherein humans are able to work themselves back to their final source of causation (God) and know God through the analogy and point of contact between Him as Infinite cause over against us as finite causes (indeed effects of His cause) [think analogia entis]; and another way was simply by understanding that words as symbols within a Covenant relation between God and humanity become the source for knowing God in an authoritative way (Nominalism).
It was this latter convention for knowing God that drove the thinking of the spitfire, the catalyst of the Protestant Reformation, Martin Luther. He repudiated the chain-of-being way, and yet was much more circumspect and concrete than the mystical way would allow for (although influences from this approach are present within the makeup of Luther’s overall attitude and approach to thinking God). As a result, Luther focused on what he called theologia crucis (theology of the cross) not analogia entis (analogy of being)—analogia entis was what gave the Roman Catholic church its authority in a hierarchical scheme for knowing God and mediating knowledge of God (as representative of Christ on earth [i.e. the Papal office] the medieval Roman Catholic church of Luther’s day was a step above [in the chain of being between God and humanity] the laity and regular people, as such they held the keys to knowledge of God). Luther’s appropriation of nominalism (theologically, not philosophically) is what allowed him to forward his idea on a theology of the cross over against the analogy of being (or also what Luther referred to as the theologia gloriae ‘theology of glory’); it cut the link between an analogy to be found in human beings vis-à-vis God. For Luther’s theology of the cross the only way for us to know God was to be found in God’s Self-revelation, which meant the words of Holy Scripture, and more radically the Word of God revealed in Jesus Christ on the cross (where Deus absconditus becomes Deus revelatus ‘the hiddeness of God becomes the revealedness of God’).
Richard Muller has written this of Luther:
One of the elements of late medieval Scotist and nominalist theology that had a profound impact on Luther was its denial of any analogy between God and man and its consequent recognition of the impossibility of formulating a rational metaphysic concerning God. All knowledge of God must rest on authoritative testimony, primarily on that of Scripture. Luther not only denied any recourse of theology to an analogia entis between God and man and insisted on the necessity of scriptural revelation, but also argued, in the light of his denial of human merit and his sense of the immediacy of Christ as revealer and savior, against any rational theologia gloriae that claimed to describe God as he is in himself and proposed that our earthly theology be a theologia crucis, conformed to the pattern of God’s revelation in Christ….
Theology of the cross could later correlate to what some have called a theology of crisis (what we find in someone like Jurgen Möltmann, and even in the early Karl Barth). God is known as we meet Him at the cross over and again; as we are depleted of our resources and thrown on the mercy of His resources revealed to us as He freely and graciously met and meets with us through the cross of His dearly beloved Son. The cross is where God’s power and reality is revealed as: God humbled and humanity exalted in the unio personalis (the singular person), Jesus Christ. The Apostle Paul was one of the foremost and earliest theologians of the cross, this typifies the attitude that a theologian of the cross thinks and lives from:
8 Brothers and sisters, we don’t want you to be unaware of the troubles that we went through in Asia. We were weighed down with a load of suffering that was so far beyond our strength that we were afraid we might not survive. 9 It certainly seemed to us as if we had gotten the death penalty. This was so that we would have confidence in God, who raises the dead, instead of ourselves. 10 God rescued us from a terrible death, and he will rescue us. We have set our hope on him that he will rescue us again, 11 since you are helping with your prayer for us. Then many people can thank God on our behalf for the gift that was given to us through the prayers of many people.
It is interesting, because when we think of the nominalist/Scotist types of dispositions that Luther had it would seem at odds with the realist/Thomist ones that we find in the theologies of Karl Barth and Thomas Torrance. I think what brings them together constructively is their (i.e. Luther’s, Barth’s, Torrance’s) focuses on a theology of the Word. Barth and Torrance, it can be said, have an a posteriori approach to thinking God; i.e. from God’s Self-revelation in Christ back up to the ontological God (so a chain-of-being way of thinking, but instead of a this chain taking link from a general conception of human being back up to God’s being, it takes link from God’s being given and revealed in Jesus Christ as a center of God’s life). I think if Luther was around when Barth and Torrance came on the scene he would approve of this kind of christologically conditioned chain-of-being thinking, because it takes the christological focus of Luther’s theology of the cross and of the Word and understands that the Covenant between God and humanity that provides genuine knowledge of God is found nowhere else but in theanthropos, the Godman, Jesus Christ. Barth and Torrance actually take the insights that Martin Luther’s via positiva ‘positive way’ (kataphatic) of doing theology emphasizes while at the same time plundering the Thomist way of knowing God non-metaphysically (as it were) from God’s reality given in Jesus Christ. What Barth and Torrance don’t take over, and now in alignment with Luther, is the Thomist chain-of-being separation of cause and effect when it comes to the person and work of Jesus Christ. This might be where Luther, Barth, and Torrance are most closely aligned; for Luther, when we see Jesus, we see God / for Barth and Torrance when we see Jesus, we see God.
 Richard A. Muller, Post-Reformation Reformed Dogmatics: The Rise and Development of Reformed Orthodoxy, ca. 1520 to ca. 1725 (Grand Rapids, Michigan: Baker Academic, 2003), 223-24.
 II Corinthians 1:8-11, Common English Bible.