Analysis:
This quatrain by Saadi Shirazi explores the themes of loyalty, friendship, and the contrast between friends and enemies. It uses a striking metaphor of a moth to convey the idea of ultimate sacrifice for a friend.

Line 1: کس عهد وفا چنانکه پروانهٔ خرد

"We've never heard of anyone who kept a promise of loyalty,"
The speaker begins by stating that they have never witnessed someone being as loyal as a wise moth. This sets up the metaphor for the rest of the quatrain.

Line 2: با دوست به پایان نشنیدیم که برد

"Like the small moth, to a friend until the end."
Here, the moth is presented as the epitome of loyalty, willing to give its life for a friend.

Line 3: مقراض به دشمنی سرش بر می‌داشت

"The scissors would sever the enemy's head,"
This line contrasts the loyalty of a friend with the harshness of an enemy. The scissors, a tool of destruction, represent the enemy who would harm without hesitation.

Line 4: پروانه به دوستیش در پا می‌مرد

"But the moth would die for its friendship."
The moth, on the other hand, is willing to sacrifice its own life for the sake of its friend. This emphasizes the depth of its loyalty.

Themes explored in the quatrain:
Loyalty in friendship: The quatrain highlights the importance of loyalty in friendship and suggests that true friends are willing to make ultimate sacrifices.
Contrast between friends and enemies: The moth and the scissors are used to represent the stark contrast between a loyal friend and a harmful enemy.
The power of sacrifice: The moth's willingness to sacrifice its life emphasizes the power of selfless love and devotion.

This quatrain is a powerful statement about the nature of friendship. By using the metaphor of a moth, Saadi suggests that true friendship is characterized by unwavering loyalty and a willingness to make ultimate sacrifices.