Barth is notorious for his doctrine of epistemology (how men know things). This is especially true with how men know God. Barth was clear that man is only able to know God through God's self-revealing (revelation) as found in the Scripture. This entails that any god derived from human reason or abstract philosophy cannot be the True God. The True God reveals Himself and in particular reveals Himself in Jesus Christ.

These in itself is a fascinating way of thinking about epistemology. But Barth claims this line of reasoning is also applicable to the words we use in our descriptions of God. When we say things like "God is love" or "God is sovereign," we must let the acts of God provide the foundation of which we define "love" and "sovereign." To use human reason or definitions is to falseify a god who is not the True God,

"We must be careful, lest we tumbled back again out of the concrete into the abstract, out of history into the realm of ideas. I would not say that God is freedom or that God is love — even though the second pronouncement is a biblical one. We do not know what love is and we do not know what freedom is; but God is love and God is freedom. What freedom is and what love is, we have to learn from him." (39)

In the midst of some interesting language, Barth's point is a simple one. When we utilize our own definitions, we use words too flippantly. Many of us know this by experience. We have all heard the "well if God was love He wouldn't <insert here>." The proof of the argument lies an abstract definition of love that is supposed to be shared by all parties. As Christians, many of us have encountered such arguments that seem to ignore God's revelation of Scripture. This is precisely Barth's point, many such statements strip "love" from God's historical example through the death of his Son (I have written practically about this trying to correct a wayward brother). 

The larger scope of Barth's point is that this can also occur with many words used in association with God. God's "sovereignty" must be defined on the basis of the Biblical witness. God's "freedom" must be seen through the lens of His free choice to create and die for His creation. It is tempting in a time where definitions matter so much — and ignored quite often — to address and confront false definitions with our more conservative, historical orthodox, and pious definitions. But when these definitions are derived apart from Scripture, they are allowed to subvert that revelation of the True God. This is a slow crafting of God in our image — and such a god is not the True God.