"The half-wise, recognizing the comparative unreality of the Universe, imagine that they may defy its Laws—such are vain and presumptuous fools, and they are broken against the rocks and torn asunder by the elements by reason of their folly. The truly wise, knowing the nature of the Universe, use Law against laws; the higher against the lower; and by the Art of Alchemy transmute that which is undesirable into that which is worthy, and thus triumph. Mastery consists not in abnormal dreams, visions and fantastic imaginings or living, but in using the higher forces against the lower—escaping the pains ofthe lower planes by vibrating on the higher. Transmutation, not presumptuous denial, is the weapon of the Master." –The Kybalion
This is the Paradox of the Universe, resulting from the Principle
of PolarityThe Seven Hermetic Principles:
6. Cause and Effect,
7. Gender. which manifests when THE ALL begins to Create—hearken to it for it points the difference between half-wisdom and wisdom.
While to THE INFINITE ALL, the Universe, its Laws, its Powers, its life, its Phenomena, are as things witnessed in the state of Meditation or Dream; yet to all that is Finite, the Universe must be treated as Real, and life, and action, and thought, must be based thereupon, accordingly, although with an ever understanding of the Higher Truth. Each according to its own Plane and Laws.
Were THE ALL to imagine that the Universe were indeed Reality, then woe to the Universe, for there would be then no escape from lower to higher, divineward—then would the Universe become a fixity and progress would become impossible.
And if Man, owing to half-wisdom, acts and lives and thinks of the Universe as merely a dream (akin to his own finite dreams) then indeed does it so become for him, and like a sleep-walker he stumbles ever around and around in a circle, making no progress, and being forced into an awakening at last by his falling bruised and bleeding over the Natural Laws which he ignored.
Keep your mind ever on the Star, but let your eyes watch over your footsteps, lest you fall into the mire by reason of your upward gaze. Remember the Divine Paradox, that while the Universe IS NOT, still IT IS. Remember ever the Two Poles of Truth the Absolute and the Relative. Beware of Half-Truths.
What Hermetists know as "the Law of Paradox" is an aspect of the Principle of Polarity. The Hermetic writings are filled with references to the appearance of the Paradox in the consideration of the problems of Life and Being.
The Teachers are constantly warning their students against the error of omitting the "other side" of any question. And their warnings are particularly directed to the problems of the Absolute and the Relative, which perplex all students of philosophy, and which cause so many to think and act contrary to what is generally known as "common sense." And we caution all students to be sure to grasp the Divine Paradox of the Absolute and Relative, lest they become entangled in the mire of the Half-Truth. With this in view this particular lesson has been written. Read it carefully!
The first thought that comes to the thinking man after he realizes the truth that the Universe is a Mental Creation of THE ALL, is that the Universe and all that it contains is a mere illusion, an unreality, against which idea his instincts revolt. But this, like all other great truths, must be considered both from the Absolute and the Relative points of view.
From the Absolute viewpoint, of course, the Universe is in the nature of an illusion, a dream, a phantasmagoria, as compared to THE ALL in itself. We recognize this even in our ordinary view, for we speak of the world as "a fleeting show" that comes and goes, is born and dies—for the element of impermanence and change, finiteness and unsubstantiality, must ever be connected with the idea of a created Universe when it is contrasted with the idea of THE ALL, no matter what may be our beliefs concerning the nature of both.
Philosopher, metaphysician, scientist and theologian all agree upon this idea—and the thought is found in all forms of philosophical thought and religious conceptions, as well as in the theories of the respective schools of metaphysics and theology. So, the Hermetic Teachings do not preach the unsubstantiality of the Universe in any stronger terms than those more familiar to you, although their presentation of the subject may seem somewhat more startling. Anything that has a beginning and an ending must be, in a sense, unreal and untrue, and the Universe comes under the rule, in all schools of thought.
From the Absolute point of view, there is nothing Real except THE ALL, no matter what terms we may use in thinking of, or discussing the subject. Whether the Universe be created of Matter, or whether it be a Mental Creation in the Mind of THE ALL—it is unsubstantial, non-enduring, a thing of time, space and change. We want you to realize this fact thoroughly, before you pass judgment on the Hermetic conception of the Mental nature of the Universe. Think over any and all of the other conceptions, and see whether this be not true of them.
But the Absolute point of view shows merely one side of the picture—the other side is the Relative one. Absolute Truth has been defined as "Things as the mind of God knows them," while Relative Truth is "Things as the highest reason of Man understands them." And so while to THE ALL the Universe must be unreal and illusionary, a mere dream or result of meditation,—nevertheless, to the finite minds forming a part of that Universe, and viewing it through mortal faculties, the Universe is very real indeed, and must be so considered. In recognizing the Absolute view, we must not make the mistake of ignoring or denying the facts and phenomena of the Universe as they present themselves to our mortal faculties—we are not THE ALL, remember.
To take familiar illustrations, we all recognize the fact that matter "exists" to our senses—we will fare badly if we do not. And yet, even our finite minds understand the scientific dictum that there is no such thing as Matter from a scientific point of view—that which we call Matter is held to be merely an aggregation of atoms, which atoms themselves are merely a grouping of units of force, called electrons or "ions," vibrating and in constant circular motion.
We kick a stone and we feel the impact it seems to be real, notwithstanding that we know it to be merely what we have stated above. But remember that our foot, which feels the impact—by means of our brains—is likewise Matter, so constituted of electrons, and for that matter so are our brains. And, at the best, if it were not by reason of our Mind, we would not know the foot or stone at all.
Then again, the ideal of the artist or sculptor, which he is endeavoring to reproduce in stone or on canvas, seems very real to him. So do the characters in the mind of the author or dramatist, which he seeks to express so that others may recognize them. And if this be true in the case of our finite minds, what must be the degree of Reality in the Mental Images created in the Mind of the Infinite?
Oh, friends, to mortals this Universe of Mentality is very real indeed—it is the only one we can ever know, though we rise from plane to plane, higher and higher in it. To know it otherwise, but actual experience, we must be THE ALL itself. It is true that the higher we rise in the scale—the nearer to "the mind of the Father" we reach—the more apparent becomes the illusory nature of finite things, but not until THE ALL finally withdraws us into itself does the vision actually vanish.
So, we need not dwell upon the feature of illusion. Rather let us, recognizing the real nature of the Universe, seek to understand its mental laws, and endeavor to use them to the best effect in our upward progress through life, as we travel from plane to plane of being. The Laws of the Universe are none the less "Iron Laws" because of the mental nature. All, except THE ALL, are bound by them. What is IN THE INFINITE MIND OF THE ALL is REAL in a degree second only to that Reality itself which is vested in the nature of THE ALL.
So, do not feel insecure or afraid—we are all HELD FIRMLY IN THE INFINITE MIND OF THE ALL, and there is naught to hurt us or for us to fear. There is no Power outside of THE ALL to affect us. So we may rest calm and secure. There is a world of comfort and security in this realization when once attained. Then "calm and peaceful do we sleep, rocked in the Cradle of the Deep" —resting safely on the bosom of the Ocean of Infinite Mind, which is THE ALL. In THE ALL, indeed, do "we live and move and have our being."
[1. From a 19th century hymn.]
Matter is none the less Matter to us, while we dwell on the plane of Matter, although we know it to be merely an aggregation of "electrons," or particles of Force, vibrating rapidly and gyrating around each other in the formations of atoms; the atoms in turn vibrating and gyrating, forming molecules, which latter in turn form larger masses of Matter. Nor does Matter become less Matter, when we follow the inquiry still further, and learn from the Hermetic Teachings, that the "Force" of which the electrons are but units is merely a manifestation of the Mind of THE ALL, and like all else in the Universe is purely Mental in its nature.
While on the Plane of matter, we must recognize its phenomena—we may control Matter (as all Masters of higher or lesser degree do), but we do so by applying the higher forces. We commit a folly when we attempt to deny the existence of Matter in the relative aspect. We may deny its mastery over us—and rightly so—but we should not attempt to ignore it in its relative aspect, at least so long as we dwell upon its plane.
The ALL is Law itself
Nor do the Laws of Nature become less constant or effective, when we know them, likewise, to be merely mental creations. They are in full effect on the various planes. We overcome the lower laws, by applying still higher ones—and in this way only. But we cannot escape Law or rise above it entirely. Nothing but THE ALL can escape Law—and that because THE ALL is LAW itself, from which all Laws emerge.
The most advanced Masters may acquire the powers usually attributed to the gods of men; and there are countless ranks of being, in the great hierarchy of life, whose being and power transcends even that of the highest Masters among men to a degree unthinkable by mortals, but even the highest Master, and the highest Being, must bow to the Law, and be as Nothing in the eye of THE ALL.
So that if even these highest Beings, whose powers exceed even those attributed by men to their gods—if even these are bound by and are subservient to Law, then imagine the presumption of mortal man, of our race and grade, when he dares to consider the Laws of Nature as "unreal!" visionary and illusory, because he happens to be able to grasp the truth that the Laws are Mental in nature, and simply Mental Creations of THE ALL. Those Laws which THE ALL intends to be governing Laws are not to be defied or argued away. So long as the Universe endures, will they endure—for the Universe exists by virtue of these Laws which form its framework and which hold it together.
The Hermetic Principle of Mentalism, while explaining the true nature of the Universe upon the principle that all is Mental, does not change the scientific conceptions of the Universe, Life, or Evolution. In fact, science merely corroborates the Hermetic Teachings. The latter merely teaches that the nature of the Universe is "Mental,"while modern science has taught that it is "Material'; or (of late) that it is "Energy" at the last analysis.
The Hermetic Teachings have no fault to find with Herbert Spencer's  basic principle which postulates the existence of an "Infinite and Eternal Energy, from which all things proceed."
[2. English polymath en.wikipedia.org/wiki/Herbert_Spencer ]
In fact, the Hermetics recognize in Spencer's philosophy the highest outside statement of the workings of the Natural Laws that have ever been promulgated, and they believe Spencer to have been a reincarnation of an ancient philosopher who dwelt in ancient Egypt thousands of years ago, and who later incarnated as Heraclitus, the Grecian philosopher who lived B. C. 500. And they regard his statement of the "Infinite and Eternal Energy" as directly in the line of the Hermetic Teachings, always with the addition of their own doctrine that his "Energy" is the Energy of the Mind of THE ALL.
With the Master-Key of the Hermetic Philosophy, the student of Spencer will be able to unlock many doors of the inner philosophical conceptions of the great English philosopher, whose work shows the results of the preparation of his previous incarnations. His teachings regarding Evolution and Rhythm are in almost perfect agreement with the Hermetic Teachings regarding the Principle of Rhythm.
So, the student of Hermetics need not lay aside any of his cherished scientific views regarding the Universe. All he is asked to do is to grasp the underlying principle of "THE ALL is Mind; the Universe is Mental—held in the mind of THE ALL." He will find that the other six of the Seven Principles will "fit into" his scientific knowledge, and will serve to bring out obscure points and to throw light in dark corners.
This is not to be wondered at, when we realize the influence of the Hermetic thought of the early philosophers of Greece, upon whose foundations of thought the theories of modern science largely rest. The acceptance of the First Hermetic Principle (Mentalism) is the only great point of difference between Modern Science and Hermetic students, and Science is gradually moving toward the Hermetic position—in its groping in the dark for a way out of the Labyrinth into which it has wandered in its search for Reality.
The purpose of this lesson is to impress upon the minds of our students the fact that, to all intents and purposes, the Universe and its laws, and its phenomena, are just as REAL, so far as Man is concerned, as they would be under the hypotheses of Materialism or Energism.
Under any hypothesis, the Universe in its outer aspect is changing, ever-flowing, and transitory—and therefore devoid of substantiality and reality. But (and note the other pole of the truth) under the same hypotheses, we are compelled to ACT AND LIVE as if the fleeting things were real and substantial. With this difference, always, between the various hypotheses—that under the old views Mental Power was ignored as a Natural Force, while under Mentalism it becomes the Greatest Natural Force. And this one difference revolutionizes Life, to those who understand the Principle and its resulting laws and practice.
So, finally, students all, grasp the advantage of Mentalism, and learn to know, use and apply the laws resulting therefrom. But do not yield to the temptation which, as The Kybalion states, overcomes the half-wise and which causes them to be hypnotized by the apparent unreality of things—the consequence being that they wander about like dream-people dwelling in a world of dreams, ignoring the practical work and life of man, the end being that "they are broken against the rocks and torn asunder by the elements, by reason of their folly." 
[3. As quoted at the top of this page.]
Rather follow the example of the wise, which the same authority states, "use Law against Laws; the higher against the lower; and by the Art of Alchemy transmute that which is undesirable into that which is worthy, and thus triumph."
Following the authority, let us avoid the half-wisdom (which is folly) which ignores the truth that: "Mastery consists not in abnormal dreams, visions, and fantastic imaginings or living, but in using the higher forces against the lower—escaping the pains of the lower planes by vibrating on the higher." Remember always, student, that "Transmutation, not presumptuous denial, is the weapon of the Master." The above quotations are from The Kybalion, and are worthy of being committed to memory by the student.
We do not live in a world of dreams, but in an Universe which while relative, is real so far as our lives and actions are concerned. Our business in the Universe is not to deny its existence, but to LIVE, using the Laws to rise from lower to higher—living on, doing the best that we can under the circumstances arising each day, and living, so far as is possible, to our biggest ideas and ideals.
The true Meaning of Life is not known to men on this plane, if, indeed, to any—but the highest authorities, and our own intuitions, teach us that we will make no mistake in living up to the best that is in us, so far as is possible, and realising the Universal tendency in the same direction in spite of apparent evidence to the contrary. We are all on The Path—and the road leads upward ever, with frequent resting places.
Read the message of The Kybalion —and follow the example of "the wise"—avoiding the mistake of "the half-wise" who perish by reason of their folly.