Barth and Torrance put a lot of effort into attacking a priori knowledge of God and establishing knowledge of God grounded in Christian experience as the dominant form of knowing God – basically, kataphatic instead of apophatic, positive over negative. Apophatic theology is seen as a form of knowledge of God grounded not in God’s self-revelation but in our conceptual schemes – we cannot say what God is, only what He is not. Torrance and Barth didn’t like this (Barth sides with Barlaam in the ‘Dogmatics’).
A big motivation here was the (in)famous point of contact – which Barth and Torrance denied quite vehemently. True knowledge of God doesn’t arise out of our own abstract speculations about God apart from His revelation – it only comes about as a result of His revelation. God not only gives knowledge of Himself out of Himself, He creates the condition necessary for knowledge of Himself.
That the heart is turned inward upon itself was and is a key point in the theology of the Reformation, and one with which I find myself in full agreement. The Truth must come from outside of man as well as the necessary condition for receiving and continuing on in the knowledge of the truth, and this means that the Teacher must also be a Healer.
The inward turning of the heart means that there is no ‘natural’ point of contact in man then. Apart from the healing which comes from without, the darkening of man’s heart by sin distorts the light of natural revelation (which is seen, distorted though it may be, in things such as broad shared moral principles common to all cultures) and leads to death.
The basic point that Barth and Torrance made, without going into the very dense language used by both of them, is that knowledge of God can only come from God in his own self-communication and self-revelation in Jesus Christ – there is no abstract knowledge of God apart from his self-revelation in Christ.