Thanks for your comment, Joshua!
To clarify, the line of thought is not "Jehovah is Satan," but that what passes as "Jesus" or "Jehovah," to Blake, is often a devil in disguise. This is in reference to his poem, "To the Accuser Who Is the God of This World":
"Truly, my Satan, thou art but a Dunce,
And dost not know the Garment of the Man.
Every Harlot was a Virgin once,
Nor canst thou ever change Kate into Nan.
"Tho’ thou art Worship’d by the Names Divine
Of Jesus and Jehovah, thou are still
The Son of Morn in weary Night’s decline,
The lost Traveller’s Dream under the Hill."
As for what Jesus would feel on the subject, I cannot say, nor do I try, as this is a piece on William Blake's view. As Blake would probably put it, as per the last 14 lines of his piece, "The Everlasting Gospel":
"The Vision of Christ that thou dost see
Is my Vision’s Greatest Enemy.
Thine has a great hook nose like thine;
Mine has a snub nose like to mine.
Thine is the friend of All Mankind;
Mine speaks in parables to the Blind.
Thine loves the same world that mine hates;
Thy Heaven doors are my Hell Gates.
Socrates taught what Melitus
Loathd as a Nation’s bitterest Curse;
And Caiphas was in his own Mind
A benefactor to Mankind.
Both read the Bible day & night,
But thou readst black where I read white."