Analysis:
This quatrain by Saadi Shirazi is a poignant expression of longing and anticipation. Let's break down each line:

Line 1: امشب نه بیاض روز برمی‌آید

"Tonight, the whiteness of day will not dawn,"
The speaker begins by emphasizing the darkness and the absence of hope for a new day. This could symbolize a state of despair or a prolonged period of waiting.

Line 2: نه نالهٔ مرغان سحر می‌آید

"Nor the morning birds' lament will come."
The absence of the morning birds' song, often associated with hope and new beginnings, reinforces the sense of despair.

Line 3: بیدار همه شب و نظر بر سر کوه

"All night long, I'm awake, gazing at the mountain,"
The speaker is depicted as being wide awake, their gaze fixed on a mountain. This could symbolize a lofty goal or a distant hope.

Line 4: تا صبح کی از سنگ به در می‌آید

"How long until the stone will fall from the mountain?"
The final line expresses a deep yearning for something to happen, a change or a breakthrough. The image of a stone falling from a mountain suggests a sudden and dramatic event.

Deeper Meaning:

This quatrain can be interpreted in several ways:

Unrequited love: The speaker might be longing for a loved one to reciprocate their feelings, and the mountain could represent the heart of the beloved.
Spiritual seeking: The speaker could be on a spiritual journey, waiting for enlightenment or a revelation.
A general sense of longing: More broadly, the quatrain can express a universal human experience of longing and anticipation.

This quatrain is a powerful expression of emotional turmoil and the human capacity for hope, even in the face of despair. The imagery of the mountain and the falling stone creates a sense of drama and anticipation.