God-centered preaching in a Text-driven Manner

"However, neither the important role of the Holy Spirit nor our faith in the triune God requires that every sermon give more or less equal time to each Person in the Godhead.  Not systematic theology but the preaching-text determines the focus of the sermon.  Systematic theology functions as the 'rule of faith' which sets the boundaries of valid interpretation; but only the text-- understood in its biblical and redemptive historical contexts-- provide the focus of the sermon." 

This was the best quote I came across in Dr. Greidanus' book, Preaching Christ From the Old Testament: A Contemporary Hermeneutical Method, 182.