SYSTEMS

John M Barry in Roger Williams and The Creation of the American Soul: Church, State, and the Birth of Liberty contrasted the beliefs of Puritans and Quakers:
"Puritans believed in predestination, that God elected saints for reasons beyond understanding, and that no human action had any bearing on election. Yet they also saw great personal struggle and living a godly as symptomatic of - although the cause of - salvation. Those who were saved worked, they did the hardest work, and Puritans no matter how confident of their own fates had to  live with the terror of doubt. They saw Christ as a historical figure, and an individual, indivisible like all other individuals. They believed that God was rational, and that the world was an ordered place. They believed that careful scholarly study of the Scripture was necessary to understand God's desires and their own tasks in the world.
 
Quakers rejected every element of those beliefs. They believed in universal redemption, and they denied that man was forever burdened with original sin. They discarded all outward forms of worship and they turned their thoughts inward, see the' light within,' the 'inner light, which they believed came from God and was part of God and lay within themselves. Indeed they raised humans nearly to divine status because they believed the Christ was inside them. They substituted human judgement for Scripture and the rule of law. They eliminated the ministry and all forms of worship. They considered men and women virtually equal and allowed women to s peak in worship. The also justified riotous behavior and even disobedience to the law. If the word 'antinomian' derives from 'against law,' this  is Antinomianism raised by orders of magnitude. Any one of these beliefs was, to Calvinists, blasphemy; taken together they certainly justified a death sentence."

British Museum
Illustrations  to Young's Night Thoughts

These statements about Puritans and Quakers in Colonial America in the late 17th century may provide some insight into Blake's resolve to create his own system rather than adopting another man's. John Milton and John Bunyan were both Puritans whose writing Blake respected, although he didn't altogether agree with them. Blake never mentions anything about Quakers although he shared most to the tenets of his religion with them. Liberty to practice religion as he choose was more important than associating himself with any group.
 

Marriage of Heaven & Hell, Plate 21, (E 42)
  "I have always found that Angels have the vanity to speak of
themselves as the only wise; this they do with a confident
insolence sprouting from systematic reasoning:
  Thus Swedenborg boasts that what he writes is new; tho' it
is only the Contents or Index of already publish'd books"
 
Jerusalem, Plate 10, (E 153)
"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
So Los, in fury & strength:"