'Without Contraries is no progression. Attraction and Repulsion, Reason and Energy, love and Hate, are necessary to human existence.' ~ 'The Marriage of Heaven and Hell'
As inhabitants of this physical plane, we are necessarily subject to the unfortunate laws that arise from our own conditioned state, the most potent of which is the divisive force of duality, which separates an essence complete in itself into two miserable halves that both hate and love each other; this is the fundamentally Platonic foundation that Blake inherits as he endeavours to construct his own visionary edifice that will potentially relieve us of this ailment.
More than anything else circumstantial, Blake was affected by Emmanuel Swedenborg, the Swedish mystic who, much like Blake himself, could allegedly converse with angels, and peer into the metaphysical realms of Heaven and Hell. Although taking an esoteric and somewhat heterodox approach to Biblical mythology, Swedenborg was essentially 'conservative', and therefore moralistic, in his theological doctrine. While Blake admits that he was positively influenced by Swedenborg in his earlier years, he eventually realizes that he represents the Church's ethical absolutism of assigning terms 'Good' and 'Evil', positing a corresponding spiritual realm for each that symbolically determines an individual's interior constitution. Hence, from this realization forward, Blake gives Swedenborg and others of his ilk the epithet, 'Angels', or those upholding the sterile status quo, and calls himself and other Orc-like spirits 'Devils', or those bringing forth new creation, thereby disturbing the prevailing order of things. Thus, a first duality is formed.
No other writing of Blake's is so profoundly satirical (not that this is the only satire – An Island in the Moon wonderfully encapsulates a Swift-esque laugh at the expense of popular philosophers) while staying true to the predominant idea being expressed than 'The Marriage of Heaven and Hell', a poem proclaiming doom and joy, death and rebirth, reason and emotion; 'Opposition is true friendship'. Devils and Angels (whom Blake also calls the Prolific and the Devouring - a further link to Platonism) are inseparably chained, and each movement that one makes is countered by the other, thus maintaining the bondage that conditions all in time and space. As this is highly reminiscent of the Urizen-Orc duality, we can expect that there is indeed a possibility of escape from this particular slavery as well.
Traditional mysticism, which is not at odds with Platonism, chiefly upholds the value of union, of the concept of achieving a state of Transcendence to the point of a metaphysical comprehension that goes beyond all physical and mental conditioning and becomes purest light, which is true reality. In addition to this, Plato outlines a cosmogonic theory in the Symposium which depicts man as a fallen being split in twain, his other half becoming trapped in feminine form. Blake adopts the latter theory with the former mystical ideal and creates a system that is well-aligned with those of tradition, and is yet perfectly unique in its own way; in his 'Book of Urizen', for example, Enitharmon becomes 'the first female now separate' when Urizen, or here the Gnostic demiurge, creates something outside of himself, namely, the world.
'I must Create a System, or be enslav'd by another Mans
I will not Reason & Compare: my business is to Create.' Jerusalem
Blake immediately encounters a problem in creating his 'system' whenever he recalls the imperative interest he has in the differentiated individual; for, while trying to merge the conditioned into the Platonic All, identity must inevitably be destroyed. Or must it? Blake questions this inevitability the same way that he questioned 'General Forms': the mass is not alive simply because it possesses universality, which of course leads to tyranny, but because of the particulars that together integrate the whole: 'General Forms have their vitality in Minute Particulars'. So, now that we discover Blake's rather ambitious project is indeed possible, our task now will be to discern how it is possible, or, to put it neatly, how exactly does the fallen man depart from his conditional duality to attain the integral 'monism' proclaimed in the Gospels?
'Neither shall they say, lo here! or, lo there! for, behold, the kingdom of Heaven is within you.' Luke 17: 21