This thesis is one particular way of clarifying how the God Christians believe in is to be understood. The key conceptual argument which runs throughout the thesis is that the distinctive relation between the world and God in Christian theology is best understood as a non-dualistic one. The ‘two’ (God + world) cannot be added up as separate, enumerable realities or contrasted with each other against some common background, since God does not belong in any category, while the creature is ontologically constituted by its relation to the Creator. In order to explore the unique character of this distinctive relation, I take up David Burrell’s invitation to turn to Sara Grant’s work on the Hindu tradition of Advaita Vedānta and the metaphysics of creation found in Thomas Aquinas. Through a careful examination of the concept of relation in Aquinas and Śaṁkara, she argues that both were issuing the same challenge: to move beyond binary oppositions between the world and God to a ‘non-dualism’ (a-dvaita) which means neither ‘one’ (i.e. God = world) nor ‘two’ (i.e. God + world). I develop her work and that of the earlier ‘Calcutta School’ by drawing explicit attention to the (Neo)Platonic themes in Aquinas which provide some of the most fruitful areas for comparative engagement with Vedānta. The fact that the world only exists in (dependence on) God means – to the Christian - that ‘God’ and ‘world’ must be ontologically distinct (since God does not exist in dependence on the world) and simultaneously means – to the Advaitin – that they cannot be ontologically separate either. The language of non-duality allows us to see, I argue, that both of these positions can be held coherently together without entailing any contradiction or disagreement at the level of fundamental ontology. What it means to be ‘world’, in other words, does not and cannot exclude what it means to be ‘God’.