Wikimedia Commons Mercy and Truth are Met Together, Righteousness and Peace Have Kissed Each Other
Error is to be replaced by truth. Error can be recognized and removed when it continues to the point that its futility is revealed by its failure to solve problems and instead to add to them. The process of removing error is performed by Los, the Imagination, into whose furnaces error is thrown to be consumed. The destruction of error depends upon giving it definite form which then can be cast off. Until an individual can see his error and release it to be destroyed, he will be in its power.
Much of Blake's writing is directed toward revealing error, not in individual men, but in the society man has created. Man's oppressive systems of government, religion, and economics result from the erroneous assumptions he makes about the value of man and the benevolence of God. The same process of exposing error in individuals in order to reveal its failure, Blake applies to every institution and philosophy he examines. Not until error has been examined, disclosed and removed can Truth and Eternity appear.
From Minna Doskow's book William Blake's Jerusalem:
"By providing form to the indefinite, science and mathematics have a redemptive use beyond their limited understanding; for they provide the concrete basis on which imagination works. So does Los's Spectre, who represents rational error, for he works under Los's compulsion for imaginative ends." (Page 57)
Jerusalem, Plate 12, (E 155) "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 55, (E 205) "For Art & Science cannot exist but in minutely organized Particulars And not in generalizing Demonstrations of the Rational Power. The Infinite alone resides in Definite & Determinate Identity Establishment of Truth depends on destruction of Falshood continually" Jerusalem, Plate 37 , (E 184) "Each Man is in his Spectre's power Untill the arrival of that hour, When his Humanity awake And cast his Spectre into the Lake" Vision of Last Judgment, (E 565) "Error is Created Truth is Eternal Error or Creation will be Burned Up & then & not till then Truth or Eternity will appear It is Burnt up the Moment Men cease to behold it I assert for My self that I do not behold the Outward Creation & that to me it is hindrance & not Action it is as the Dirt upon my feet No part of Me." Jerusalem, Plate 42, (E 189) "Los answerd. Righteousness & justice I give thee in return For thy righteousness! but I add mercy also, and bind Thee from destroying these little ones: am I to be only Merciful to thee and cruel to all that thou hatest[?] Thou wast the Image of God surrounded by the Four Zoa's Three thou hast slain! I am the Fourth: thou canst not destroy me. Thou art in Error; trouble me not with thy righteousness. I have innocence to defend and ignorance to instruct: I have no time for seeming; and little arts of compliment, In morality and virtue: in self-glorying and pride." Jerusalem, Plate 41 , (E 188) And Ely, Scribe of Los, whose pen no other hand Dare touch! Oxford, immortal Bard! with eloquence Divine, he wept over Albion: speaking the words of God In mild perswasion: bringing leaves of the Tree of Life. Thou art in Error Albion, the Land of Ulro: One Error not remov'd, will destroy a human Soul Repose in Beulahs night, till the Error is remov'd Reason not on both sides. Repose upon our bosoms Till the Plow of Jehovah, and the Harrow of Shaddai Have passed over the Dead, to awake the Dead to Judgment. But Albion turn'd away refusing comfort." Vision of Last Judgment, (E 562) "All Life consists of these Two Throwing off Error & Knaves from our company continually & recieving Truth or Wise Men into our Company Continually."Psalms 85
 Surely his salvation is nigh them that fear him; that glory may dwell in our land.
 Mercy and truth are met together; righteousness and peace have kissed each other.
 Truth shall spring out of the earth; and righteousness shall look down from heaven.