Steven Mathewson has a short post about Calvin’s approach to preaching. Here is Calvin’s philosophy about God-centered preaching:
When we profess to believe in one God, under the name of God is understood a single, simple essence, in which we comprehend three persons, or hypostases. Therefore, whenever the name of God is mentioned without particularization, there are designated no less the Son and the Spirit than the Father.
So for Calvin, to talk about God in his sermon was to talk about Christ. This brings up an interesting question: Is “God-centered” preaching adequate, or does each sermon have to be “Christ-centered” (i.e., “redemptive”)?