Analysis:

This quatrain by Saadi Shirazi is a beautiful expression of love and admiration for a beloved whose beauty is beyond description.

The Beloved's Transcendent Beauty: The speaker is comparing the beloved to natural phenomena like the cypress, sun, and moon, but finds these comparisons inadequate. This suggests that the beloved's beauty is so extraordinary that it transcends any earthly comparison.
The Power of a Sigh: Even a simple sigh, often associated with longing and sorrow, is deemed insufficient to capture the beloved's essence.
The Universal Quest: The speaker suggests that countless people are searching for the beloved, indicating a universal longing for something beyond the ordinary.
The Paradox of the Journey: The final line creates a paradox. If the path to the beloved were known, there would be no need for a journey. This suggests that the true beauty of the beloved lies not in the destination but in the journey itself.

Themes:

Divine Beauty: The beloved's beauty is portrayed as almost divine, beyond human comprehension.
The Journey of Love: The quest for the beloved is seen as a spiritual journey.
The Paradox of Desire: The desire for something unattainable is a central theme.

Deeper Meaning:
This quatrain suggests that true beauty is often elusive and defies description. The beloved becomes a symbol of something greater than oneself, perhaps a spiritual ideal or a representation of perfection. The journey to find this beloved is a metaphor for the human search for meaning and purpose.

This quatrain is a celebration of the power of love and the beauty of the unattainable. It invites the reader to contemplate the nature of beauty and the human longing for something greater than themselves.