This immediately brings in the fundamental point that I want to make in this book, that there are indeed two different ways by which God acts. We tend to restrict our idea of God's activity to one, that he intervenes intrusively into the world, effectively by miracle. This is like the entry into the world of Jesus as the incarnate second Person of the Godhead. I want to emphatically affirm this, but to add that he acts in a second way, by his presence in everything, such as by underpinning its very existence. Just as I suggested in my previous book, that the action of God in the world is fundamentally Trinitarian, I now want to say that it is also fundamentally theistic, that God in his very nature is both transcendent and immanent, and so that he acts in a way reflecting this duality. Theism is not just belief in God, as its name might suggest (from Greek theos, "god"), but should be understood in this specific way. This means on the one hand that he acts intrusively in accordance with his transcendence, maintaining essential difference and separation from the world, and on the other he acts by his essential presence in accordance with the second. The Christian understanding is of a transcendent yet immanent God (Blocher 1984:281). Augustine said that God is superior summo meo et interior intimo meo (“higher to me than my highest part and more intimate to me than my most inward part”). We are related to God both as I-it (transcendent) and I-thou (more immanent) (as Martin Buber stressed). I want to stress that in fact the two are not just complementary, but each demands the other. And again, I will point out that these two aspects are not only complementary, but essential to each other. Trinitarianism really demands theism, and, to an extent, the opposite is also true.
These two aspects are fundamentally and distinctively Christian. While most religions in the world include belief in divinity, it is only Christianity that holds that God is Trinity. Moreover, it is really only Christianity, although also to an extent Judaism, that holds that God is theistic and so acts theistically. Wenham (1974:173) here comments that "biblical theism towers over every other system of human thought".
Although it is not often appreciated, the particular form of belief does strongly affect society. J D Unwin in a book written in 1934 surveyed 86 societies and found in all a link between absolute monogamy and society energy. Decline followed change in morals (Yancey 2002:18). Likewise the particular view on the relation between transcendence and immanence has wide-ranging effects. Erickson (1998c:257) notes that it affects the views of providence, humanity as in the image of God, salvation, the church, eschatology, the nature of the Bible, and the understanding of creation. This is by no means exhaustive. I therefore want to describe why Christianity is theistic, and how the two aspects are brought together.
This book is however not just a foray into the doctrine of God, fascinating though that is, and indeed central to Christian thought, which is what "theology" is all about. The temptation of theology, and especially theology of a more philosophical kind, is that it tends to become abstract and unrelated to the real world. It may well be important, which any thought about God must be, and true, but it is really not so helpful unless it is applied to human life. Here I touch on what has been at the centre of my theological thought for the whole of my career, that theology must be applicable to human life. Niebuhr was convinced of the applicability of Christianity to every social situation (Grenz & Olsen 1992:102). And indeed, it must be inherently so, simply because the heart of the Christian understanding of humanity is indeed that people were created in the image of God.