“To plead the organic causation of a religious state of mind, then, in refutation of its claim to possess superior spiritual value, is quite illogical and arbitrary, unless one have already worked out in advance some psycho-physical theory connecting spiritual values in general with determinate sorts of physiological change.”

Statements after the Solvay Conference of 1927, as quoted in Physics and Beyond (1971) http://www.edge.org/conversation/science-and-religion by Werner Heisenberg
Context: At the dawn of religion, all the knowledge of a particular community fitted into a spiritual framework, based largely on religious values and ideas. The spiritual framework itself had to be within the grasp of the simplest member of the community, even if its parables and images conveyed no more than the vaguest hint as to their underlying values and ideas. But if he himself is to live by these values, the average man has to be convinced that the spiritual framework embraces the entire wisdom of his society. For "believing" does not to him mean "taking for granted," but rather "trusting in the guidance" of accepted values. That is why society is in such danger whenever fresh knowledge threatens to explode the old spiritual forms. The complete separation of knowledge and faith can at best be an emergency measure, afford some temporary relief. In western culture, for instance, we may well reach the point in the not too distant future where the parables and images of the old religions will have lost their persuasive force even for the average person; when that happens, I am afraid that all the old ethics will collapse like a house of cards and that unimaginable horrors will be perpetrated. In brief, I cannot really endorse Planck's philosophy, even if it is logically valid and even though I respect the human attitudes to which it gives rise.
Einstein's conception is closer to mine. His God is somehow involved in the immutable laws of nature. Einstein has a feeling for the central order of things. He can detect it in the simplicity of natural laws. We may take it that he felt this simplicity very strongly and directly during his discovery of the theory of relativity. Admittedly, this is a far cry from the contents of religion. I don't believe Einstein is tied to any religious tradition, and I rather think the idea of a personal God is entirely foreign to him. But as far as he is concerned there is no split between science and religion: the central order is part of the subjective as well as the objective realm, and this strikes me as being a far better starting point.