Two Great Lights

In Genesis 1:16 we read about the 'two great lights'.  Blake used the Sun and
the Moon and inserted into them a world of meanings.

Like all natural phenomena Blake used the Sun and the Moon to express
many things.   He found two kinds of Sun, a natural sun and an eternal Sun:

(Erdman 465-6)
What it will be Questiond When the Sun rises do you not  see a round Disk of 
fire somewhat like a Guinea O no no I see an Innumerable company of the 
Heavenly host crying Holy Holy Holy is the Lord God Almighty

From Auguries of Innocence (ErdmaN 490)
If the sun and moon should doubt,
they'd immediately go out.

Penseroso and L' Allegro Plate 3

 From  MILTON'S L'ALLEGRO III
 Blake states: 
"The Great Sun is represented clothed in Flames 
Surrounded by the Clouds in their Liveries, in their 
various Offices at the Eastern Gate. beneath in Small 
Figures Milton walking by Elms on Hillocks green The 
Plowman. The Milkmaid The Mower whetting his Scythe. 
& The Shepherd & his Lass under a Hawthorn in the Dale"
 
The Great Sun is the Spiritual Sun the source of light not 
measured in wavelengths and frequencies. The spiritual 
sun is the source of true existence which partakes of the 
eternal and infinite energy of life. It announces its presence 
by increased clarity of perception expressed in truth, mercy 
and grace.

Blake used the Lark as the symbol of the messenger of Los; 
he uses the symbol of the sun as Los himself as both the 
message and the source of the message.
In this picture Blake uses scale as one of the means to 
distinguish between the natural world and the Eternal world. 
In the third illustration to L'Allegro Blake follows the text he is 
illustrating but changes the emphasis by using most of the page 
 to present the sun at his eastern gate. The occupants of the 
mundane world, including Milton, appear at the bottom of the 
page as small easily overlooked figures. 

Four levels of existence can be distinguished in the image. 
The pastoral level of this earth is represented in the strip at the 
bottom of the page. Surrounding the sun is the level of Beulah as 
dominated by the feminine. Within the disc of the sun is the fiery 
transformative level. The primary figure which overlaps the other 
three layers is the Great Sun in his Human or Divine form.