Analysis:

This quatrain by Saadi Shirazi expresses a deep, consuming love that has become an integral part of the speaker's being. It depicts a state of complete devotion and submission to the beloved. Let's break down each line:

Line 1: ای در دل من رفته چو خون در رگ و پوست

"O you who have entered my heart like blood into veins and skin,"
The speaker compares their love for the beloved to blood coursing through their veins, suggesting that the love is as essential to their existence as blood is to the body. This line conveys a sense of deep intertwining and unity.

Line 2: هرچ آن به سر آیدم ز دست تو نکوست

"Whatever befalls me from your hand is good,"
This line expresses a profound level of acceptance and submission. Regardless of the circumstances or the pain inflicted, the speaker believes that anything that comes from the beloved is ultimately good. This suggests a masochistic or self-destructive tendency in love, a willingness to endure pain for the sake of the beloved.

Line 3: ای مرغ سحر تو صبح برخاسته‌ای

"O bird of dawn, you have risen,"
The speaker addresses the bird, symbolizing the arrival of dawn and the beginning of a new day.

Line 4: ما خود همه شب نخفته‌ایم از غم دوست

"But we have not slept all night for the sorrow of our beloved."
This line contrasts the awakening of the natural world with the sleepless night of the lover due to their sorrow. It highlights the intensity of their longing and the pain of separation.

Themes explored in the quatrain:

Unconditional love: The speaker's love is so deep that they accept any pain or suffering that comes from the beloved.
Suffering for love: The speaker is willing to endure pain and sleepless nights for the sake of their love.
Unity with the beloved: The speaker feels a deep connection to the beloved, as if they are one and the same.

This quatrain is a powerful expression of romantic love, characterized by a deep sense of devotion, submission, and suffering. The speaker is willing to endure any pain, believing that their beloved's love is worth it.