Why do I reject natural theology? Why is this such a big deal for me you might wonder. Because I don’t think this is your normal theological locus; I think it is in a class all its own. Theological ontology-epistemology are the bases upon which God-talk can occur to begin with. How we understand these bases will say much about how we understand the God we portend to speak of and more importantly after (if that’s the order we end up following). So why I do reject the idea that human beings can come to a knowledge of God outside of God’s Self-revelation in Jesus Christ?
John Webster, even as he is imbibing the spirit of classical Reformed theology, helps to elucidate why someone like me would reject natural theology. As an aside: it’s not just “Barthians” who reject natural theology, it is Bavinckians, and many of the Post Reformed orthodox themselves (see Muller, PRRD). As Webster identifies there are two prongs that inhibit a natural knowledge of God: 1) God’s ineffability, and 2) our fallen and finite capacities. He writes:
A third principle requires a little more extensive explanation. A Christian doctrine of creation is doubly inhibited: by the ineffability of its object, and by the limits of fallen intelligence. The doctrine is chiefly concerned, no so much with causal explanation of what is as with contemplation of the fact that what is might not have been and yet is, and of the infinite bliss of God who lies on the other side of that ‘might not have been’. The doctrine’s core, in other words, is not cosmology but theology proper — God’s ‘invisible nature’ (Rom. 1.20), which, even when manifest in the visibilia of created reality, exceeds comprehensive intelligence (a point obscured when teaching about creation is annexed by natural theology). Knowledge of the creator and of creation is creaturely knowledge; in knowing the creator and his act, and ourselves as creatures, we do not transcend our creaturely condition, but repeat it: ‘no point of contemplation can be found outside Himself’, Hilary reminds his readers. More particularly, in this matter, creaturely knowledge is directed to an agent wholly surpassing us, to an act from whose occurrence we were absent: ‘Where were you when I laid the foundations of the earth?’ (Job 38.4). Moreover — as God’s question to Job discloses — what restricts us is not simply the finiteness of created intelligence but its fallenness and ‘futility’ (Rom. 1.21), its darkening of counsel by words without wisdom (Job 38.2). Knowledge of the creator and of ourselves as creatures is a casualty of the fall: we will not honour the creator (Rom. 1.21), we will not acknowledge ourselves to be his creatures. Fallen intelligence tends away from God, in the forgetfulness and impatience (Ps. 106.13). To know its creator, reason must be healed by repentance and the suffering of divine instruction, by which love of God is made to grow. The rule which governs teaching about the Trinity, and therefore about creation as one of its extensions, is: love alone restores knowledge. Love, furthermore, is the end of theological contemplation of the creator and his work. The goal of the redeemed mind’s exercise in this matter is ‘that [God] may himself be sought, and himself be loved.’ Or, as a later Augustinian put it, the task of trinitarian theology is ‘to manifest what is expressly revealed in the Scripture concerning God the Father, Son, and Holy Ghost; so as that we may duly believe in him, yield obedience unto him, enjoy communion with him, walk in his love and fear, and so come at length to be blessed with him for evermore.
On the latter locus I am reminded of the Petrine wisdom:
3 His divine power has given us everything we need for a godly life through our knowledge of him who called us by his own glory and goodness. 4 Through these he has given us his very great and precious promises, so that through them you may participate in the divine nature, having escaped the corruption in the world caused by evil desires.5 For this very reason, make every effort to add to your faith goodness; and to goodness, knowledge; 6 and to knowledge, self-control; and to self-control, perseverance; and to perseverance, godliness; 7 and to godliness, mutual affection; and to mutual affection, love. 8 For if you possess these qualities in increasing measure, they will keep you from being ineffective and unproductive in your knowledge of our Lord Jesus Christ. 9 But whoever does not have them is nearsighted and blind, forgetting that they have been cleansed from their past sins.
God —> Knowledge of God —> Through Participation —> Leading to Moral and Noetic Transformation in Faith as Knowledge —> To Orthopraxis —> Grounded in the Love of God in Christ. Sum: All of this movement is grounded in God’s choice to be God for us in Jesus Christ. From this springs the only possibility wherein genuine knowledge of God can obtain. None of this would occur without the reality that God is Love.
These represent some of the realities why I reject a theologia naturalis or natural theology as a preamble to a genuine knowledge of God. For one thing it is unnecessary to posit a natural theology—at least for the Christian—because by definitional reality Christians are already Christians by being those in encounter with the living Word as by the Holy Spirit (I Cor. 12.3). It’s a redundancy for those who already know the voice of God (his sheep cf. Jn 10) to attempt a look elsewhere for a foundational knowledge of God. True, philosophy and its lexicon is undeniably present in the history and development of theologics; but the grammar that has reified the various philosophies is a heavenly sui generis one that has no parallel, and needs none when the Christian knows the voice of their Shepherd. This is why I think Barth’s analogia fidei/relationis (faith-relation) de jure is the better way to go when attempting to be a theologian of the cross.
 John Webster, God Without Measure: Working Papers In Christian Theology: Volume 1: God And The Works Of God (London: Bloomsbury-T&T Clark, 2015), 83-4.
 II Peter 1.3-9, NIV.