In Jung’s writing a complex was the name he gave to a group of feelings, associations and behaviours which had a sort of semi-autonomous status in the human mind. Complexes play a huge role in spirituality but that role is … well, complex really … but we will unravel this at our Numinous meeting.
From Jung, The symbolic life 149-153
Ladies and Gentlemen, that leads me to something very important—the fact that a complex with its given tension or energy has the tendency to form a little personality of itself. It has a sort of body, a certain amount of its own physiology. It can upset the stomach. It upsets the breathing, it disturbs the heart—in short, it behaves like a partial personality. For instance, when you want to say or do something and unfortunately a complex interferes with this intention, then you say or do something different from what you intended. You are simply interrupted, and your best intention gets upset by the complex, exactly as if you had been interfered with by a human being or by circumstances from outside. Under those conditions we really are forced to speak of the tendencies of complexes to act as if they were characterized by a certain amount of will-power. When you speak of will-power you naturally ask about the ego. Where then is the ego that belongs to the will-power of the complexes? We know our own ego-complex, which is supposed to be in full possession of the body. It is not, but let us assume that it is a centre in full possession of the body, that there is a focus which we call the ego, and that the ego has a will and can do something with its components. The ego also is an agglomeration of highly toned contents, so that in principle there is no difference between the ego-complex and any other complex.
 Because complexes have a certain will-power, a sort of ego, we find that in a schizophrenic condition they emancipate themselves from conscious control to such an extent that they become visible and audible. They appear as visions, they speak in voices which are like the voices of definite people. This personification of complexes is not in itself necessarily a pathological condition. In dreams, for instance, our complexes often appear in a personified form. And one can train oneself to such an extent that they become visible or audible also in a waking condition. It is part of a certain yoga training to split up consciousness into its components, each of which appears as a specific personality. In the psychology of our unconscious there are typical figures that have a definite life of their own.2
 All this is explained by the fact that the so-called unity of consciousness is an illusion. It is really a wish-dream. We like to think that we are one; but we are not, most decidedly not. We are not really masters in our house. We like to believe in our will-power and in our energy and in what we can do; but when it comes to a real show-down we find that we can do it only to a certain extent, because we are hampered by those little devils the complexes. Complexes are autonomous groups of associations that have a tendency to move by themselves, to live their own life apart from our intentions. I hold that our personal unconscious, as well as the collective unconscious, consists of an indefinite, because unknown, number of complexes or fragmentary personalities.
 This idea explains a lot. It explains, for instance, the simple fact that a poet has the capacity to dramatize and personify his mental contents. When he creates a character on the stage, or in his poem or drama or novel, he thinks it is merely a product of his imagination; but that character in a certain secret way has made itself. Any novelist or writer will deny that these characters have a psychological meaning, but as a matter of fact you know as well as I do that they have one. Therefore you can read a writer’s mind when you study the characters he creates.
 The complexes, then, are partial or fragmentary personalities. When we speak of the ego-complex, we naturally assume that it has a consciousness, because the relationship of the various contents to the centre, in other words to the ego, is called consciousness. But we also have a grouping of contents about a centre, a sort of nucleus, in other complexes. So we may ask the question: Do complexes have a consciousness of their own? If you study spiritualism, you must admit that the so-called spirits manifested in automatic writing or through the voice of a medium do indeed have a sort of consciousness of their own.
Lionel Corbett also has a great take on this …
Archetypes, Complexes and our spiritual life
Because the archetype carries out two simultaneous functions, our spirituality is closely bound to our psychological development. First, because the archetype is at the centre of our complexes, the archetype is important in the overall structure of the psyche and affects our emotional health. At the same time, because of its numinosity, the archetype also affects our spiritual life. Consequently, our psychology and spirituality, the personal and the transpersonal, interpenetrate in the complex – here, psychology and spirituality become synonymous. Since the archetype is at the core of both our complexes and our numinous experiences, the same archetype may be at the root of our emotional suffering and also generate an authentic spiritual experience. Consequently, our spirituality is not an isolated process that can be relegated to weekend worship services. Neither can it be fully contained within a dogmatic system of thought. Our spirituality develops organically as we mature. Ideally this means that is contains less and less childhood residues.
From Psyche and sacred by Lionel Corbett p83