Blake offers us four levels of existence in time, plus a level of existence outside of time: Great Eternity.
The first thing to focus on in considering Great Eternity is that Eternity is not time. Eternity is not an extension of time. Eternity may contain time, but time cannot contain Eternity. Eternity may interact with time. There is a flexibility in Eternity that does not exist in time, because time is a restraint allowing only sequential experience (access.) Without time multiplicity and unity are not contradictory. In Eternity essence remains, appearances fluctuate.
"Then those in Great Eternity met in the Council of God
As one Man for contracting their Exalted Senses
They behold Multitude or Expanding they behold as one
As One Man all the Universal family & that one Man
They call Jesus the Christ & they in him & he in them
Live in Perfect harmony in Eden the land of life
Consulting as One Man above the Mountain of Snowdon Sublime"
This passage in Night the First of the Four Zoas (Page 21) uses the word one, five times in seven lines. It seems that Blake wanted to emphasize that in Great Eternity there is no division. Blake does not envision Great Eternity as a static place but as one in which the movement does not result in separation. Envisioning Eternity is impossible for mortals, but these are characteristics Blake offers:
1 Contracting their Exalted Senses, they see Multitude (Four Zoas, Page 21)
2 Expanding they see as One (Four Zoas, Page 21)
3 Visions of Human Life & Shadows of Wisdom & Knowledge are expandable (Milton, Plate34)
4 War & Hunting are the Two Fountains of the River of Life (Milton, Plate35)
5 Universal Brotherhood exists in Eternity (Four Zoas, E300, Lines 3.4-3.5)
6 Ideas may not be slain (they are the Divine Members) (Milton, Plate35)
7 Every particular form is the Divine Vision (Jerusalem, Plate 54)
8 Every form Emanates its Light which is its Garment (Jerusalem, Plate 54)
9 There is Continual Forgiveness of Sins and Perpetual Mutual Sacrifice (Jerusalem, Plate 61, Line 23-4)
The Eternal can be expressed but it cannot be contained.
We can be present to it, and it can be present to us as imagination and inspiration.
Forgiveness and Brotherhood are expressions of the Eternal.
Divisions and limitations disappear in Eternity.
Life and Light participate in the great exchange.
The energies of the mind and body and spirit interact freely and cooperatively in Great Eternity.