Blake's Trees

Like most of Blake's images you may find a source for them in the Good Book. Looking there we find two particular trees in the 3rd chapter of Genesis, and several other trees scattered throughout.

The Tree of Life:

"For the cherub with his flaming sword is hereby commanded to
leave his guard at the tree of life, and when he does, the whole
creation will be consumed, and appear infinite. and holy whereas
it now appears finite & corrupt."
MHH 14 Erdman 39 (read on!) "

"He views the Cherub at the Tree of Life, also the Serpent,
Orc the first born coild in the south: the Dragon Urizen:
Tharmas the Vegetated Tongue even the Devouring Tongue:
A threefold region, a false brain: a false heart:
And false bowels: altogether composing the False Tongue,
Beneath Beulah......"
Jerusalem 14:2 E158

And Jerusalem plate 86, line 18; E244:
"I see thy Form O lovely mild Jerusalem, Wingd with Six Wings....
here all the Tribes of Israel I behold
Upon the Holy Land: I see the River of Life & Tree of Life
I see the New Jerusalem descending out of Heaven"

Lacoon prose at E274:
"ART is the Tree of LIFE GOD is JESUS"

A Vision of the Last Judgment (Erdman 562):
" The Temple stands on the Mount of God from it flows on each
side the River of Life on whose banks Grows the tree of Life
among whose branches temples & Pinnacles tents & pavilions
Gardens & Groves Display Paradise with its Inhabitants walking up
& down in Conversations concerning Mental Delights"

And on and on!

Turning now to the other tree in Genesis:

The Tree of the Knowledge of Good and Evil

Bible scholars have dealt in various ways with this one. ("But of the tree of the knowledge of good and evil, thou shalt not eat of it: for in the day that thou eatest thereof thou shalt surely die." [Genesis 2:17]

Some have referred to 'the original sin' as the feliz culpa ("the fortunate Fall).

Here's Blake:
"Self Evident Truth is one Thing and Truth the result of
Reasoning is another Thing Rational Truth is not the Truth of
Christ but of Pilate It is the Tree of the Knowledge of Good & Evil"
(Annotations of Bacon; E621)

The Tree of Mystery

The early Blake used this metaphor 14 times, 13 of them in The Four Zoas, but never in the large prophetic works (or anywhere after ca 1800).

In The Book of Ahania Blake gave us a clue of what he meant by Mystery and the Tree of Mystery:

Here's chapter III of The Book of Ahania:

"I: The Globe shook; and Urizen seated

On black clouds his sore wound anointed
The ointment flow'd down on the void
Mix'd with blood; here the snake gets her poison        

2: With difficulty & great pain; Urizen
Lifted on high the dead corse:
On his shoulders he bore it to where
A Tree hung over the Immensity

3: For when Urizen shrunk away                          
From Eternals, he sat on a rock
Barren; a rock which himself
From redounding fancies had petrified
Many tears fell on the rock,
Many sparks of vegetation;                             
Soon shot the pained root
Of Mystery, under his heel:
It grew a thick tree; he wrote
In silence his book of iron:

Till the horrid plant bending its boughs    
Grew to roots when it felt the earth
And again sprung to many a tree.

4: Amaz'd started Urizen! when
He  beheld  himself compassed round
And high roofed over with trees             
He arose but the stems stood so thick
He with difficulty and great pain
Brought his Books, all but the Book

PLATE 4
Of iron, from the dismal shade

5: The Tree still grows over the Void
Enrooting itself all around
An endless labyrinth of woe!

6: The corse of his first begotten          
On the accursed Tree of MYSTERY:
On the topmost stem of this Tree
Urizen nail'd Fuzons corse."
(Erdman 86-87)

Would you like to guess what he meant with the Tree of Mystery?
I would suppose that he was talking about the tree with the
cursed 'apple', otherwise referred to as the Tree of the Knowledge
of Good and Evil.

For Blake 'Mystery' connoted (false) Religion, those who chose what
is good and what is evil and coerced the gullible into believing they
represented the authority of God:

We started with MHH 14. So here are the words of Plate 11:
"The ancient Poets animated all sensible objects with Gods or
Geniuses calling them by the names and adorning them with the
properties of woods, rivers, mountains, lakes, cities, nations,
and whatever their enlarged & numerous senses could percieve.
   And particularly they studied the genius of each city &
country.  placing it under its mental deity.
   Till a system was formed, which some took advantage of &
enslav'd  the vulgar by attempting to realize or abstract the
mental deities from their objects: thus began Priesthood.
   Choosing forms of worship from poetic tales.
   And at length they pronounced that the Gods had orderd such things
Thus men forgot that All deities reside in the human breast."