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

[16] And God made two great lights; the greater light to rule the day, and the lesser light to rule the night: he made the stars also.
[17] And God set them in the firmament of the heaven to give light upon the earth,
[18] And to rule over the day and over the night, and to divide the light from the darkness: and God saw that it was good.
[19] And the evening and the morning were the fourth day. 

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.