Northrop Frey wrote on page 251 of FEARFUL SYMMETRY:
"The rising Orc has been visualized as killing a dragon and as pushing a rock from his tomb, but neither if these images is really exact. When a new life is born, a new form emerges from unorganized matter, and the "victory" of the rising Orc is the only kind of victory that is possible: the conquest of the creator over his material, the reduction of a monster to a shape. We must now superimpose another pattern on this one. Just as Satan or the monster of death is overcome by Orc, so Orc himself is a monster of natural life (hence his association with the serpent) who must be in turn be overcome, or shaped into a form, by someone else. And as Orc shapes life out of death, so this someone shapes the conscious vision out of life which is the imagination proper, the character or identity, and so constructs a Being from the Becoming. Orc brings life into time; the shaper brings life in time into eternity, and as Orc is the driving power of Generation, so his shaper is the power of Regeneration. This shaper is the driving force of all of Blake's later poems, Los the blacksmith, the divine artificer, the spiritual form of time, the Holy Spirit which spoke by the prophets."
Los at the forge with Enitharmon and Orc
MILTON Plate 24 reads:
"Los is by mortals nam'd Time. Enitharmon is nam'd Space
But they depict him bald and aged who is in eternal youth
All powerful and his locks flourish like the brows of morning
He is the Spirit of Prophecy, the ever apparent Elias.
Time is the mercy of Eternity; without Times swiftness
Which is the swiftest of all things: all were eternal torment:
All the Gods of the Kingdoms of Earth labour in Los's Halls.
Every one is a fallen Son of the Spirit of Prophecy
He is the Fourth Zoa, that stood arou[n]d the Throne Divine."
"Orc, the amorphous cub whom Los has to lick into shape, is Los' first-born son, as Los is the Holy Spirit or incubating power from whom all life proceeds. And as no life reaches eternity without first going through the physical world, the young Orc is bound by Los to the latter."
So through the fall, Los and Orc each become the prisoner of the other that the work of regeneration may ultimately be accomplished.