Blake was a mystic - was divinely inspired - had direct access to and received evidence of reality.
Mystics provide us with what might be termed objective evidence; but most mystics are just as prone to misunderstand, misinterpret, and falsely-systematize objective evidence evidence as are you and I.
Blake was also a Man, of knowledge incomplete and fallible, and (perhaps more than usually) prone to hatred and resentment.
So, we can benefit greatly from the inspired wisdom of Blake - but need also to recognize that Blake's own understanding of Blake's own wisdom was rather poor - which is why so much of his writing is essentially meaningless (and hardly even attempts to be meaningful).
But if we consider The Marriage of Heaven and Hell from " Without Contraries is no progression" up to the end of the Proverbs of Hell "Enough! or Too much!"; then we are confronted with as profound and as concentrated a catalogue of truth as human hand has penned.
(With the exception of the Apostles.)
Our task is to regard this as divinely-inspired evidence; but to edit-out Blake's own false interpretations and systematizations of this evidence.
And this is what we must do with all (true) mystical insight - whether from the Prophets and Saints; or from other modern Christian (or at least self-identified Christian) mystics like Pascal, Traherne, Swedenborg, Ralph Waldo Emerson, Rudolf Steiner and William Arkle.