It would be a cheap play on words to set doubt against unity, for one can fall into the one but not into the other, and so they are not concepts of the same nature, since even opposition requires a certain likeness.
Unity as a principle is an important insight in how we see the world: that everything belongs together, that there are no discrete events, only processes, no drop of water, only the sea, that the fact of existence binds every living being together, and we could go on. This character of the universe, traceable to a single principle, can be interpreted cosmologically, in terms of the theory of creation or the theory of existence, but also morally, and within man's web of social relations. We may also say that the recognition of belonging together is the guarantee of harmony.
Plato expressed this belonging together through the existence of originally spherical human beings, whose pride Zeus set out to break by splitting their bodies in two, and so man and woman came to be. Could this have been the first appearance of doubt? Could a moral fault, conceit, have led to the split, to the loss of fullness? Is this why everyone seeks his other half? How much despair springs from this split?
A split is a loss of value. Torn cloth can be stitched together, but the mark remains. A torn banknote is withdrawn from circulation. A cracked jug is worthless, and a split state of consciousness is an illness. Perhaps dividedness is the sign of having fallen out of divine harmony, of alienation, and it rightly gives rise to despair. The aggravated form of despair is doubt.
What does one doubt? For a long time, others, God, spiritual processes, people, at times truths. But perhaps all doubt can be traced back to one innermost self-division, when a man doubts not outer factors but himself. Let us not think merely of little faith or a lack of self-confidence, which is the simpler case. If a man attends a good spiritual school, he is taught that excessive self-confidence is not right, but neither is a lack of it, for both are in fact egoism, only with the sign reversed. Real doubt is an existential crisis, when a man does not know for what reason, in what way and to what end he should live. When we cannot justify our own existence. This lack of support, outer and inner, can lead to utter nihilism, and, as we know, attack is the best form of defence, so we can best conceal how unresolved our own existence is by calling other things, phenomena or people into question.
Sadly, doubting nowadays is not merely a figure of style, although a performer who shows himself doubting and inwardly torn may win easy success. This element of style has taken fatal hold of modern man. Long ago the philosophy of the sceptics still held truth to be knowable, and scepticism was rather a means of knowing, but there is also the kind of doubt that does not inquire but distrustfully rejects everything.
Doubt is the inevitable companion of spiritual processes. As long as it acts as a spur, as a thirst for knowledge, as inquiry, it has its positive role, but when it disputes the practice, the master or God, it becomes a watershed. If a man falls victim to his doubts, he strays, but if he weathers the times of doubt, he becomes immune to doubting. The doubting man is not happy in the world, neither in this life nor in the next. Never mind if man doubts the existence of God, so long as the good Lord does not lose trust in man.
Now, in the vision of fullness, duality – and not doubt – must carry at least as much weight as experiencing unity. Duality, too, is a cosmic principle, and at the level of principle it means not a split, and thus decay, but multiplication, that is, increase. We may also say that unity and duality are the two sides of the same coin, inseparable from each other. Together they form the coin, one heads, the other tails, and what is more, the coin also bears an inscription on its rim, which is not doubt but divine love.