Blake's pictures in The Book of Thel supplement the ideas he presents in the text. In this copy of the Book of Thel from the Library of Congress, Rare Books Collection, we can read the text and view the pictures together as they were meant to be understood.
Book of Thel
First you may notice that although Blake talks of clouds, lilies, worms and clods he pictures human beings. This reinforces the idea that he is not talking about nature in general or specific parts of it, but about humans and aspects of the psyche. So the answers given by the lily and her associates are our answers, the way we explain the puzzling inconsistencies of our experience to ourselves. We may open or close ourselves to Blake's reasonings, or we may try them on for size before searching elsewhere.
On the title page we notice that Thel, the shepherdess is the observer not the participant. The sexual imagery which many people notice in Thel is apparent in the male and female soaring images on this page. Erdman (The Illuminated Blake) says 'these lovers are the human form of the Dew and the Cloud'. The flowers on this page are not the lilies of the poetry but the pasqueflower 'said to require the wind to open the petals' for fertilization.
The images surrounding the word Thel at the top of the page 3 bring to mind the four Zoas although the characters remain to be fully developed as Blake continues to write. You may recognize the soaring lady with the flying infant from the Preludium to the First Book of Urizen - it is not Urizen but a tie to his book. The man in the sky reaching for the eagle is a reminder of Los who like the eagle can represent imagination. To the right carrying shield and flaming sword is the Zoa of emotions, Luvah, who for the first time is mentioned in this poem. Reclining on the seedpod of grain is a figure in a position reminiscent of the 'renovated man' who appears above the man entering death's door in the engraving for Blair's The Grave. The picture for The Grave and the appearance of Tharmas as man's body will be later inventions but the fourfold split is already present.
Plate 4 shows Thel looking very much like the Lilly with whom she converses. Plate 5 is all text. On Plate 6 which concerns the worm, we see an image of an infant on the ground and the matron clod soaring in the air as she discusses with Thel how 'we live not for ourselves.' Thel demonstrates her astonishment. In plate 7 Thel, the observer as usual, watches the mother and child, clod and worm, as they play together. Children happily ride the serpent as the poem ends with
If this poem is seen to address the issues which specifically face women, those of being expected to be gentle and receptive rather than assertive and active, we may contrast it to the poem "how sweet I roamed". The latter poem represents the adolescent beginning to be aware of opportunities and abilities and facing society's limitations on the expanding possibilities. In the poem Thel, the young woman seems to be offered limited possibilities to begin with: humility and service, basking in another's attention, not reasoning, and living for others instead of for herself. This may be what Thel rejects: accepting a subservient role in a household or in a society that undervalues women. Was Blake commenting on the role of women as well as the human condition of being born into the material world?
The poem does not specifically mention the world of Generation, but the images present Generation as the world to which Thel is invited. The rejection of the feminine role or the fear of sexuality may be impediments to Thel's accepting the opportunity to enter the material world. Read the words, read the pictures, read in the context of Blake's work, read according to your own light.