From Pierre Berger's 1915 book William Blake, Poet and Mystic:
"As one reads his [Blake's] books, one sees his theories becoming gradually clearer and more complete. Different works explain each other. None of them is complete in itself: all must be known and borne in mind if any one is to be read properly. Even when he wrote the first, Blake had dimly in his mind the ideas which were to fill his latest books. His theories do not seem to have changed as he grew older. They undergo development: they are expressed in different terms; but at bottom they remain the same. Just as a seed contains all the germs from which the plant will receive its shape, the flowers their colours, and the fruit its flavour, so it is with Blake and with the development of his genius.
His work can be studied in either of two quite different ways. We might take his books one by one and examine, in each successively, his philosophical ideas, his prophetic theories, and the manner of their expression. We should thus follow step by step the development of his mind. We should see how his thought becomes more and more complex, while still keeping its original direction, and how, at the same time, his symbolic exposition of it becomes more and more enigmatic, as if, by a strange perversity, in proportion as the prophet found more to say, the artist were seeking more obscure forms of expression, to make his meaning more and more incomprehensible. We should find, at the beginning, ideas that are relatively simple and natural, and human feelings common to all, expressed clearly and with much poetic talent—at times even with flashes of genius. Later on, this genius becomes entangled in the complexities of mystical vision, and its splendid gifts are, so far as true poetry is concerned, entirely lost. At the outset, the breath of mysticism fans the poetic fire: in the end, it becomes a tempest, scattering the flames, which it lifts here and there into huge columns, but gradually extinguishing them and leaving only a vast pile of ashes smouldering in darkness.
I prefer, however, to take another way of reaching the same conclusions. I shall try to sketch the broad outlines of his philosophy and to describe his mystical world, as far as these may be elucidated from the whole body of his work. I shall then consider his method of poetic expression, strictly from the poetic point of view, and trace the factors that conduced to its rapid growth, its wonderful flowering and its slow decay under the invading influences of mysticism and symbolism. And so I shall separate the study of his doctrines from that of their expression, without concerning myself too much with the successive developments of either, but reserving these for a short subsequent examination of his books in their chronological order." (Page 65)
Berger described how he created his system for studying Blake. He looked at the whole and at the individual parts. He followed the development, but in the end he evaluated Blake's thought in terms of his own criteria for success.
Blake first expressed his interest in systems in Marriage of Heaven & Hell. The creation of systems became metaphor for building and discarding the mental constructs which control our ability to perceive. A system, even a poor one, served man until he recognized its inadequacy. Man was not able to abandon a system until it failed cataclysmically. The effort which Blake saw as going into the creation and exploration of systems was really directed at self-understanding and freeing oneself from false reasoning powers he called the Selfhood.
Marriage of Heaven & Hell, PLATE 11, E(38) "The ancient Poets animated all sensible objects with Gods or Geniuses calling them by the names and adorning them with the properties of woods, rivers, mountains, lakes, cities, nations, and whatever their enlarged & numerous senses could percieve. And particularly they studied the genius of each city & country. placing it under its mental deity. Till a system was formed, which some took advantage of & enslav'd the vulgar by attempting to realize or abstract the mental deities from their objects: thus began Priesthood. Choosing forms of worship from poetic tales. And at length they pronounced that the Gods had orderd such things. Thus men forgot that All deities reside in the human breast. Jerusalem, Plate 10, (E 152) "And this is the manner of the Sons of Albion in their strength They take the Two Contraries which are calld Qualities, with which Every Substance is clothed, they name them Good & Evil From them they make an Abstract, which is a Negation Not only of the Substance from which it is derived A murderer of its own Body: but also a murderer Of every Divine Member: it is the Reasoning Power An Abstract objecting power, that Negatives every thing This is the Spectre of Man: the Holy Reasoning Power And in its Holiness is closed the Abomination of Desolation Therefore Los stands in London building Golgonooza Compelling his Spectre to labours mighty; trembling in fear The Spectre weeps, but Los unmovd by tears or threats remains I must Create a System, or be enslav'd by another Mans I will not Reason & Compare: my business is to Create Yet ceasd he not from labouring at the roarings of his Forge With iron & brass Building Golgonooza in great contendings Till his Sons & Daughters came forth from the Furnaces At the sublime Labours for Los. compelld the invisible Spectre Plate 11 To labours mighty, with vast strength, with his mighty chains, In pulsations of time, & extensions of space, like Urns of Beulah With great labour upon his anvils, & in his ladles the Ore He lifted, pouring it into the clay ground prepar'd with art; Striving with Systems to deliver Individuals from those Systems; That whenever any Spectre began to devour the Dead, He might feel the pain as if a man gnawd his own tender nerves." Jerusalem, Plate 12, (E 155) "Yet why despair! I saw the finger of God go forth Upon my Furnaces, from within the Wheels of Albions Sons: Fixing their Systems, permanent: by mathematic power Giving a body to Falshood that it may be cast off for ever." Jerusalem, Plate 35 , (E 181) "It is the Gate of Los. Withoutside is the Mill, intricate,dreadful And fill'd with cruel tortures; but no mortal man can find the Mill Of Satan, in his mortal pilgrimage of seventy years For Human beauty knows it not: nor can Mercy find it! But In the Fourth region of Humanity, Urthona namd[,] Mortality begins to roll the billows of Eternal Death Before the Gate of Los. Urthona here is named Los. And here begins the System of Moral Virtue, named Rahab." Jerusalem, Plate 43 , (E 191) "And thus the Voice Divine went forth upon the rocks of Albion I elected Albion for my glory; I gave to him the Nations, Of the whole Earth. he was the Angel of my Presence: and all The Sons of God were Albions Sons: and Jerusalem was my joy. The Reactor hath hid himself thro envy. I behold him. But you cannot behold him till he be reveald in his System Albions Reactor must have a Place prepard: Albion must Sleep The Sleep of Death, till the Man of Sin & Repentance be reveald."