Three fundamental categories for theologizing are nature, grace, and glory. These terms indicate things you’ve already thought about before, but they don’t quite map onto other terms you might already know.
Nature is what a thing is in itself. Human nature is a created good, a thing with its own integrity and a recognizable completeness in itself. You can’t quite call it independent, because every nature you’ve ever encountered is a created nature which owes its being to God. But nature, the realm of created goods, has to have a relative independence from God in that it genuinely has existence as something distinct from the creator. You didn’t have to exist, and it’s worth thanking God for the gratuity and bonus of your sheer existence.
Grace, on the other hand, is more. It is something given to nature from beyond. When God gives grace to nature, he elevates nature beyond its own resources and makes it participate in something superior to itself. As Aquinas would say in his Aristotelian tone of voice, a creature does not have within its finite nature the potential to reach an infinite end, so if finite creatures (nature) are to enjoy fellowship with the infinite God, it will have to be by grace. Human nature may have its own finite telos (end), but salvation is the perfection of human nature in the true end of man, which is the glorification and enjoyment of God. Is there a natural desire for what is beyond nature? Is the structural integrity of human nature some sort of structural openness to God? “It takes God to be a man,” said Major W. Ian Thomas.
All the best arguments about salvation (soteriology) happen at the point where theologians try to describe what grace does to nature. Does grace destroy nature? Replace nature? Correct nature? Perfect nature? Call nature forth to its highest possibilities? Strengthen nature? Wound nature? Cooperate with nature?
The nature-grace nexus is the place where major theological decisions are made, whether we know the terms or not. The first steps in theological anthropology are fundamentally the steps taken here, in assuming a position on nature and grace.
But the two-step dialectic of nature and grace is not enough to take in the whole biblical revelation. Every page of the Bible is about eschatology, the end, and if you omit the eschatological element, grace makes no sense. Glory is the traditional theological term for the kind of eschatology you can reckon with as a factor in theological anthropology.
What can you say about glory, when you’ve already been obedient to the heavenly vision and exhausted your vocabulary of wonder in praising God’s grace? But there it is: glory. Everything floats and shines and revolves around this center which is everywhere. Glory is the meaning of everything, the reason there is nature. Nature is for glory. And grace is glory under the conditions of nature.
Grace only makes its appearance as a kind of overlap between nature and glory. As Thomas Aquinas aptly put it, “Grace is nothing else than a kind of beginning of glory in us.” (Summa Theologiae II.II.xxiv.3). The theologians who have been brave enough to think this through all the way and sober enough to stay sane have all agreed that you have to begin at the end. You have to start with glory and work back through grace to nature, because glory is bigger. Irenaeus knew that the glory of God is a man alive, and that men live to see God. Augustine knew that the way was the truth was the life. Calvin makes it sound like he’s beginning at the absolute beginning, “before the foundation of the world,” but he has heaven in mind the whole time. Barth not only knew it, but knew it by its true name.
Now abides nature, but God gives grace and God gives glory. We experience grace now as “a kind of beginning of glory in us.”