Analysis:

This quatrain by Saadi Shirazi is a subtle and evocative piece that uses the metaphor of a mole on a beloved's face to convey the passage of time and the changes that come with age.

Line 1: خالی که مرا عاجز و محتال بکرد

"A mole that made me weak and helpless,"
The mole is personified here and is described as having a powerful effect on the speaker. It suggests that the beloved's beauty mark has had a profound impact on the speaker's emotions and actions.

Line 2: خطی برسید و دفع آن خال بکرد

"A line arrived and repelled that spot."
The appearance of a line on the face, perhaps a wrinkle, is seen as counteracting the effect of the mole. This suggests that the passage of time can diminish the impact of even the most striking features.

Line 3: خال سیهش بود که خونم می‌ریخت

"That dark mole was drinking my blood,"
The mole is described as "drinking the speaker's blood," a hyperbolic way of expressing the intense emotional attachment the speaker feels to the beloved.

Line 4: ریش آمد و رویش همه چون خال بکرد

"A beard grew and turned his whole face like that mole."
The final line suggests that as the beloved ages, the mole becomes less prominent and the entire face takes on a similar character. This implies that the passage of time can unify and harmonize different aspects of a person's appearance.

Themes explored in the quatrain:

The passage of time: The quatrain is a meditation on the passage of time and the changes it brings to our appearance and our relationships.
Beauty and aging: The mole and the line represent different aspects of beauty and how they change over time.
The power of love: The speaker's intense attachment to the beloved is evident throughout the quatrain, suggesting that love can transcend physical beauty.

This quatrain is a subtle and poignant exploration of the themes of beauty, aging, and love. Through the metaphor of a mole, Saadi conveys the complex emotions and thoughts that accompany the passage of time and the changes it brings to our relationships.