Analysis:
This quatrain by Saadi Shirazi expresses a deep and unwavering devotion to a friend, despite the friend's flaws. The speaker is willing to endure any hardship or pain that comes from this friendship, emphasizing the strength and loyalty of their bond.

Line 1: گویند رها کنش که یاری بدخوست

"They say, 'Leave him, for he is a bad friend.'"
The speaker introduces the idea that others are advising them to end the friendship.

Line 2: خوبیش نیرزد به درشتی که دروست

"His goodness is not worth the harshness he shows."
Here, the others are justifying their advice by highlighting the friend's negative qualities.

Line 3: بالله بگذارید میان من و دوست

"By God, let me be between my friend and myself,"
The speaker rejects the advice of others and expresses a desire for privacy in their relationship with the friend.

Line 4: نیک و بد و رنج و راحت از دوست نکوست

"Both good and bad, pain and comfort, from my friend are good."
In this final line, the speaker declares that they find value in both the good and bad aspects of the friendship, suggesting a deep level of acceptance and understanding.

Themes explored in the quatrain:
Unconditional friendship: The speaker's love for their friend is unconditional, extending beyond the friend's flaws.
Individuality and autonomy: The speaker asserts their right to make their own choices about the friendship, despite the advice of others.
Acceptance: The speaker accepts both the good and bad aspects of the friendship, suggesting a mature and understanding perspective.

This quatrain is a powerful statement about the nature of friendship. The speaker's unwavering loyalty and acceptance of their friend's flaws highlight the enduring power of human connection.