If we hear “God is love” and think it means “Love is God”, as in thinking that our idea of love is God, we have reduced God to an idea, a concept. And since everyone has a slightly different concept of love–and some not so slightly, but very different–these little idols we make of our concept of love cannot come close to the reality of God.
God is always bigger than an idea, than our concept of him. It could be no other way. The beauty of this is that contact with God will always broaden, expand, and fill out our idea of love, making our concept of love move always in a direction away from idolatry.