The Cultivation of Anger

The principal theme of "A Poison Tree" is not anger itself but how the suppression of anger leads to the cultivation of anger. Burying anger rather than exposing it and acknowledging it, according to "A Poison Tree," turns anger into a seed that will germinate. Through the cultivation of that seed, which is nourished by the energy of the angry person, wrath grows into a mighty and destructive force.

The Wrathfulness of the Old Testament God

An implicit theme of "A Poison Tree" is that the god of the Old Testament is a god of wrath, cunning, jealousy, and guile. Blake presents this theme in the poem by alluding to the story of the Fall in Genesis. The tree in Blake's poem is intended to remind the reader of the Tree of the Knowledge of Good and Evil. The bright apple represents the fruit on that tree, which God forbids Adam and Eve to eat, thus making it more appealing. The garden into which the foe steals signifies the Garden of Eden, where Adam and Eve act in stealth and disobey God. The attitude of the speaker himself is to be understood as a reflection of God's attitude. By showing the speaker of the poem acting in a way reminiscent of God, Blake is showing God to be not a god of love but a cruel god and is thus criticizing the commonly held idea of God.

Suppression versus Expression

To the extent that "A Poison Tree" teaches a lesson and asserts a moral proposition rather than offering a critique of a theological system, the lesson is less concerned with anger than with demonstrating that suppressing the expression of feelings leads to a corruption of those feelings, to a decay of innocence, and to the growth of cunning and guile. Repeatedly in Songs of Experience, not just in "A Poison Tree," Blake argues that the religious doctrines intended to train people, especially children, in virtue are cruel and cause harm. In addition, Blake depicts those who implement religious discipline as sadistic.

Hypocrisy

Blake called the original draft of "A Poison Tree" "Christian Forbearance," suggesting that what is meant to appear as a gentle attitude is often a mask for disdain and anger. Furthermore, Blake believed that the attitudes of piety that adherents of conventional Christianity were taught to maintain actually led to hypocrisy, causing people to pretend to be friendly and accepting when they were not. The righteousness that the conventional religion prescribed, Blake believed, allowed people to hide evil intent and to perform evil deeds, such as stifling the healthy growth of children, under the cover of appearing virtuous.