Analysis:

This quatrain by Saadi Shirazi expresses an intense and consuming love, particularly focusing on the overpowering nature of longing.

Line 1: هر وقت که بر من آن پسر می‌گذرد

"Whenever that boy passes by me,"
The first line establishes the situation where the speaker is repeatedly encountering the object of their affection.

Line 2: دانی که ز شوقم چه به سر می‌گذرد؟

"Do you know what happens to me out of longing?"
This line directly addresses a listener, perhaps the beloved or a confidant, asking them to understand the depth of the speaker's longing.

Line 3: گو هر سخن تلخ که خواهی فرمای

"Say whatever bitter words you want,"
The speaker invites harsh words or criticisms, suggesting that their love is so strong that even negative comments would not diminish their feelings.

Line 4: آخر به دهان چون شکر می‌گذرد

"In the end, they will taste like sugar to me."
This line emphasizes the speaker's intense devotion. No matter how harsh the words, their love will make even bitterness seem sweet.

Themes explored in the quatrain:

Intense love and longing: The quatrain is a vivid portrayal of overwhelming love and the suffering caused by unfulfilled desire.
The power of love: The speaker's love is so powerful that it can transform even bitter words into sweetness.
Unconditional devotion: The speaker's willingness to endure any hardship for the sake of their love demonstrates an unwavering devotion.

This quatrain beautifully captures the intensity of romantic love. It showcases the speaker's vulnerability and their willingness to endure pain for the sake of their beloved.