Christian theology consists of variations on common themes. What makes one theologian or system distinct from another is not always a substantive difference; often it is the eloquence or beauty on display, or the particular articulation of a doctrine, or an especial emphasis on a certain aspect of the whole rather than another.
This is an under-appreciated aspect of doing theology. If every systematic theology sets out to offer something substantially new, we’re in trouble. When you read a work of theology, the author is treading on very well-worn paths. Many others have already covered this terrain. What other book has generated the level of commentary and secondary literature that the Bible has? That doesn’t mean it is wrong-headed for a theologian to take his or her best shot at it. But it does suggest that the author shouldn’t be aiming for—and we shouldn’t be expecting—theological innovation or novelty. Emphasizing a certain overlooked element, articulating a doctrine with fresh verve and clarity, demonstrating its coherence with other aspects of truth—these are more modest and appropriate goals.