When reviewing Barth's descriptions of the Trinity and Luther's, it occurred to me that the two theologians use very different metaphors to describe the Trinitarian life. Barth's description is "unveiled, unveiler, unveiling." Luther's is "speaker, word spoken, hearing."
Barth's metaphors have to do with seeing, Luther's with hearing. This makes sense in light of how they understand divine revelation. Barth views divine revelation as the unfolding of a single subject (God) in an act of revealing himself in time. He does this by echoing his eternal decision to be "one who loves in freedom" in the temporal narrative of Jesus. This temporal narrative is "unveiling" is further echoed in "Jesus, Bible and proclaimed Word" which echoes the Father, Son and Spirit, as "revealed, revealer, revealing." Barth's view of revelation is essentially analogical. Analogy has to do with a kind of visible similitude between things and therefore envisions human knowledge (following Aristotle) as a kind of intellectual vision.
Luther's theology works on the basis of hearing. In other words, God's agency manifests itself through the law which is present and visible through all creation. Human can observe how the world works and see what God's legal will is. They can also see this in the horrific act of judgment that God causes to take place in salvation history. Nevertheless, God promises his grace and enacts under his act of judgment and under act of weakness. The supreme one is the cross. We are told that Jesus is God and that the cross is an act of grace. Nevertheless, all we see is weakness (a weak, beaten and dying Christ) and condemnation (i.e. a symbol of Israel's sin and continuing exile). Contrary to this, we hear "surely he was the Son of God" and "today you will be with me in paradise." Consequently, revelation's hiddenness is transcended only by hearing the Word. Proper knowledge of God is set against analogical and visible knowledge of God, and placed in the realm of hearing.
It therefore makes sense that Luther views God primarily in terms of hearing rather than vision or unveiling.