till it bore an apple bright" refers to the tree of wisdom that bears fruit, traditionally believed to be apples. In the Bible, Adam and Eve eating the apple leads to the introduction of original sin into the world. The poem's speaker is parallel to the serpent in The Garden of Eden; he lures his foe near the tree and tempts him to eat the poison apple. The speaker's anger has filled him with evil, like the serpent, who is also evil. This biblical allusion suggests that anger produces a metaphorical fruit that harms those tempted into eating it. Blake's allusion also suggests that the fruit both trees produce leads to a cycle of anger and hatred. However, when emotions like anger are expressed, the cycle is broken, and no more harm is done. This aligns with the Romantic's belief that acknowledging emotion rather than suppressing it can lead to peace. Unlike beliefs from the Age of Enlightenment, Blake proves that raw emotion, rather than logic alone, can be compelling.

"I was angry with my friend:
I told my wrath, my wrath did end."

However, in the later verses, the speaker transforms. Instead of resolving his emotions, he nurtures them:

"And I watered it in fears,
Night and morning with my tears;
And I sunned it with smiles,
And with soft deceitful wiles."

The speaker's actions become much more intentional and sinister. He smiles while he tends to this tree that bears a poison fruit. What he does is deliberate and thought out.

The foe, in contrast, is unsuspecting and naive. This characterization sets up his downfall, as he is found "outstretched beneath the tree" by morning. Through these characterizations, Blake explores the consequences of unexpressed anger.

The diction in "A Poison Tree" is straightforward. This gives it a rhythmic quality. Blake uses simple, everyday language and modest rhymes like "shine" and mine" or "night" and "bright". This diction makes his poem accessible for a broad audience to understand the message.

The mood of this poem is dark, bitter, and secretive. The anger and bitterness the narrator feels towards his enemy eventually leads to this enemy's demise.

"And I watered it in fears,
Night and morning with my tears;
And I sunned it with smiles,
And with soft deceitful wiles."

Here, the tree is a metaphor for wrath, which the speaker cultivates through secrecy. Rather than expressing his anger openly, he feeds it with "fears," "tears," and "deceitful wiles," allowing it to grow unchecked. Eventually, this wrath bears fruit in the form of an apple, a symbol of revenge.