This Plate has top and bottom pictures with the text in between.
this Gate cannot be found
PLATE 35 
By Satans Watch-fiends tho' they search numbering every grain
Of sand on Earth every night, they never find this Gate.
It is the Gate of Los. Withoutside is the Mill, intricate,
And fill'd with cruel tortures; but no mortal man can find
Of Satan, in his mortal pilgrimage of seventy years
For Human beauty knows it not: nor can Mercy find it! But
In the Fourth region of Humanity, Urthona namd, Mortality begins
to roll the billows of Eternal Death
Before the Gate of Los. Urthona here is named Los.
And here begins the System of Moral Virtue, named Rahab.
Albion fled thro' the Gate of Los, and he stood in the Gate.
Los was the friend of Albion who most lov'd him. In
His eternal station, he is the twenty-eighth, & is four-fold.
Seeing Albion had turn'd his back against the Divine Vision,
Los said to Albion, Whither fleest thou? Albion reply'd.
I die! I go to Eternal Death! the shades of death
Hover within me & beneath, and spreading themselves outside
Like rocky clouds, build me a gloomy monument of woe:
Will none accompany me in my death? or be a Ransom for me
In that dark Valley? I have girded round my cloke, and on my feet
Bound these black shoes of death & on my hands, death's iron
God hath forsaken me, & my friends are become a burden
A weariness to me, & the human footstep is a terror to me.
Los answerd, troubled: and his soul was rent in twain:
Must the Wise die for an Atonement? does Mercy endure Atonement?
No! It is Moral Severity, & destroys Mercy in its Victim.
So speaking, not yet infected with the Error & Illusion,
In the second paragraph we see Urthona namd, Mortality begins to roll the billows
of Eternal Death Before the Gate of Los. Urthona here is named Los: so who is
Urthona? It's typical of Blake to use one word with several (or many!) meanings.
In this case Urthona is Los (fallen); his name is (also) Mortality; he goes
on to explicate: 'the system of Moral Virtues, named Rahab.'
This is another of the many explanations of the meaning of Fallenness in Blake's myth
then we have an amplified description of Los.
The dialogue between Albion and Los could be considered a meditation on the meaning of
the suffering and death of Jesus on the cross, with sentiments that many of us share.
There are two. The top one shows a satanic old king surrounded by bat-wings on his horse shooting an arrow from a three fold bow at--what? (In nightmares I see myself shooting
arrows at my three sons.) In the text of this plate Blake tells us in line 1 that Satan's watch fiends cannot find the Gate of Los. There it is. (look also at this little picture in the Gates of Paradise.) Blake has sent his own arrow at the Pale Horse.
Below the setting sun resembles the cogwheels (satanic mills) of Plate 22 (Erdman1 301).