Either God is a Mystery or He is nothing at all. - Walter Terence Stace

Thus when Plotinus speaks of "the flight of the alone to the Alone," and the positivist or the empiricist asserts that these words are meaningless, he is right. Yet this does not import that the words are nonsense locutions, mere senseless noises which a man makes like a cough or a sneeze though it is possible that this is what the positivist intends. If this were so, it would be impossible to explain why generations of men have quoted those famous words. The explanation is that the words evoke in us a measure of the same experience which the author of them had. Our experience may be but a dim reflection of what was in him bright and clear. Our spirits vibrate faintly in unison with the soul of the great mystic, as a tuning fork vibrates faintly in response to the sound of the clear bell. But it is our own spontaneous experience which is evoked; it is not his experience which is communicated to us. His words are as grappling irons let down into the depths of our subconsciousness, which draw our own inner experiences nearer to the conscious threshold. But they are not, for most of us, drawn above the threshold. They remain below the surface faintly visible. Therefore they appear at the upper levels of our consciousness as faint hints, glimpses, and sometimes as mere vague feelings.

Thus we see that mysticism naturally, though not necessarily, becomes intimately associated with whatever is the religion of the culture in which it appears.

How is it possible for both naturalism and religion - atheism and theism, if you prefer it - to be but two sides of one truth, is the same as the problem how God can be both being and non-being, as one of the most ancient religious and mystical insights proclaims he is, or how he can be both the Eternal Yes and the Eternal Nay, as Böhme affirmed.