One of the major heresies at work today in the church is Pelagianism. The chief error of Pelagius (http://www.newadvent.org/cathen/11604a.htm) was that he did "not regard the wrath of God, (and Pelagianism( constructs for itself such a God who is merciful" (pg. 174) Now, that is striking! The idea that God is merciful is heresy! Before telling me that I am wrong, let me explain myself (and with that, Brunner and Luther's position). The problem with the idea that God is merciful is that in today's age, we want to think of God as only merciful. That is clearly not the case if we read Scripture faithfully.
The flip side of this heresy is to think that God is only un-merciful, that the Divine is only here to crush us and condemn us to punishment. In some churches, we stress the doctrine of Hell and torment and create a God that does not love, and only punishes. This too leaves us with an incomplete picture of God.
What we should understand is that God is both merciful and full of wrath. The mercy of God flows from His right hand, while the wrath of God flows from his left. This is an important distinction made by Martin Luther and carried on by Brunner and Barth. There are two sides (at least!) to God and His will.
Luther explained this by positing that God is both Deus Absconditus and Deus Revalatus. God is both Hidden and Revealed to us simultaneously. God is a mystery to us, and is truly the mysterium tremendum", the Tremendous Mystery that we cannot fathom and cannot know, if it were not for the second part, which is that God reveals Himself to us. This means, that on one side, God is separate from us, apart from us, and not with us.God is, in a word, Holy.
If it were not for the fact that He is a God who Reveals, we would know nothing about Him. He would be reduced down to a concept that would not be necessary to know about. He would become Aristotle's Unmoved Mover or First Cause, that which started the world, and absconded.
However, we cannot approach such a God that is Holy if He did not veil Himself. This leads us to Luther's second distinction, that God is both Deus Nudus and Deus Velatus. "The Deus nudus is that naked Majesty, the of whom is intolerable for the sinful creature." (pg. 171) Brunner goes on talking about 'the naked God', saying that "it is impossible that human weakness should grasp and be able to bear the High Majesty of God" (pg. 172) With this, we should think of Moses on the mount when God passes by, unveiled, revealing only his back, lest Moses die. It is not that we cannot intellectually comprehend the naked God, but that we cannot even see the full majesty, lest we die. "Hence, "he who does not wish to fall on this stone and be broken to pieces, let him beware, and not deal with God 'nakedly' apart from His Word and His promise" (pg. 172)
The Naked God refers "to God apart from Christ" (pg. 172), apart from His revelation. It is then the work of the Naked God, of His Left Hand to pour out judgment and wrath on humanity. "Sin", not God's Will or Nature, "the resistance of man, is the reason why God must do this 'strange work' (Opus alienum), why He must show Himself and express Himself as the wrathful God." (pg. 169) It is not because God is wrathful that he punishes. It is because God is Holy and man resists to be Holy that God pours out wrath and anger. "Sin obliges Him 'to turn his back on man', to do His work 'on the left hand', instead of His work of grace 'on the right hand." (pg. 169) The wrath of God "attains its end, in the repentance and faith of the sinner, it is in very deed the most characteristic work of the Grace of God." (pg. 169) Brunner, through Luther, here is making a claim that needs to be listened to. The wrath of God is not punishment for punishment sake, but punishment as chastisement. It is not wrath, it is grace.
God, due to His Grace, becomes the veiled, through His Revelation (that is to say, through Christ), so that He can become known to us. He becomes known to us "not as the unveiled naked Majesty, but only in this veiled form as Love." (pg. 172) God, in His Nature, is Love, not wrath. Brunner here quotes Luther, who says "His Heart and Thoughts are full of love and nothing else." (Pg. 171)
We must then be guarded when talking about God being a God of love. For love "does not rejoice in unrighteousness, but rejoices with the truth" (1 Corinthians 13:6, NASB). Love only exists where Truth and Righteousness exist. "In Jesus Christ alone, God makes Himself known as He really is. In Him God shows Himself to us as 'an abyss of eternal love'. The revelation and the communication of this love, the work of free grace is 'God's proper work, His opus proprium." (Pg. 168-169)
Thus, it is not that God is wrathful or merciful. It is that God is loving. Maybe it is right to say that in the end, Love wins.