I've just started reading Alice Bailey's "Treatise on White Magic" which is really about the spiritual journey. I was particularly struck by the simplicity of the four postulates that are stated in the introduction:
"This book will be based also upon four fundamental postulates which must be admitted by the student of the succeeding pages as providing an hypothesis worthy of his consideration and trial. No true investigator of the Ageless Wisdom is asked to give blind adherence to any presentation of truth; he is asked, however, to have an open mind and seriously to weigh and consider the theories and ideals, the laws and the truths which have guided so many out of darkness into the light of knowledge  and experience. The postulates might be enumerated as follows and are given in the order of their importance.
I. First, that there exists in our manifested universe the expression of an Energy or Life which is the responsible cause of the diverse forms and the vast hierarchy of sentient beings who compose the sum total of all that is. This is the so-called hylozoistic theory, though the term but serves to confuse. This great Life is the basis of Monism, and all enlightened men are Monists. "God is One" is the utterance of truth. One life pervades all forms and those forms are the expressions, in time and space, of the central universal energy. Life in manifestation produces existence and being. It is the root cause, therefore, of duality. This duality which is seen when objectivity is present and which disappears when the form aspect vanishes is covered by many terms, of which for the sake of clarity, the most usual might be here listed:
• Spirit - Matter
• Life - Form
• Father - Mother
• Positive - Negative
• Darkness - Light
Students must clearly have this essential unity in mind e'en when they talk (as they needs must) in finite terms of that duality which is everywhere, cyclically, apparent.
II. The second postulate grows out of the first and states that the one Life, manifesting through matter, produces a third factor which is consciousness. This consciousness, which is the result of the union of the two poles of spirit and matter is the soul of all things; it permeates all substance or objective energy; it underlies all forms, whether it be the form of that unit of energy which we call an atom, or the form of man, a planet, or a solar system. This is the Theory of Self-determination  or the teaching that all the lives of which the one life is formed, in their sphere and in their state of being, become, so to speak, grounded in matter and assume forms whereby their peculiar specific state of consciousness may be realized and their vibration stabilized; thus they may know themselves as existences. Thus again the one life becomes a stabilized and conscious entity through the medium of the solar system, and is essentially, therefore the sum total of energies, of all states of consciousness, and of all forms in existence. The homogeneous becomes the heterogeneous, and yet remains a unity; the one manifests in diversity and yet is unchanged; the central unity is known in time and space as composite and differentiated and yet, when time and space are not (being but states of consciousness), only the unity will remain, and only spirit will persist, plus an increased vibratory action, plus capacity for an intensification of the light when again the cycle of manifestation returns.
Within the vibratory pulsation of the one manifesting Life all the lesser lives repeat the process of being, - Gods, angels, men, and the myriad lives which express themselves through the forms of the kingdoms of nature and the activities of the evolutionary process. All become self-centered and self-determined.
III. The third basic postulate is that the object for which life takes form and the purpose of manifested being is the unfoldment of consciousness, or the revelation of the soul. This might be called the Theory of the Evolution of Light. When it is realized that even the modern scientist is saying that light and matter are synonymous terms, thus echoing the teaching of the East, it becomes apparent that through the interplay of the poles, and through the friction of the pairs of opposites light flashes forth. The goal of evolution is found to be a gradual series of light demonstrations. Veiled and  hidden by every form lies light. As evolution proceeds, matter becomes increasingly a better conductor of the light, thus demonstrating the accuracy of the statement of the Christ "I am the Light of the World".
IV. The fourth postulate consists of the statement that all lives manifest cyclically. This is the Theory of Rebirth or of reincarnation, the demonstration of the law of periodicity.
Such are the great underlying truths which form the foundation of the Ageless Wisdom - the existence of life, and the development of consciousness through the cyclic taking of form."
Variations of these postulates, I think, are also at the root of A Course In Miracles, Seth material, Lazaris material, Edgar Cayce material, and many other perspectives on the spiritual journey.