Analysis:
This quatrain by Saadi Shirazi is a playful exploration of beauty, modesty, and the nature of attraction. Let's break down the lines:

Line 1: آنان که پریروی و شکر گفتارند

"Those who are graceful and sweet-tongued"
The speaker is referring to people who are both beautiful and eloquent.

Line 2: حیفست که روی خوب پنهان دارند

"It's a pity they hide their beautiful faces."
The speaker expresses regret that such beautiful people would choose to conceal their appearance.

Line 3: فی‌الجمله نقاب نیز بیفایده نیست

"Nevertheless, a veil is not entirely useless"
Despite the beauty of these people, the speaker acknowledges that there is a purpose to veils.

Line 4: تا زشت بپوشند و نکو بگذارند

"So that they may cover the ugly and reveal the beautiful."
The speaker suggests that veils can be used to hide imperfections and highlight positive attributes.

Deeper Meaning:
This quatrain can be interpreted in several ways:

Beauty and modesty: The quatrain explores the tension between the desire to showcase beauty and the value of modesty.
The power of appearance: The speaker suggests that appearance can be a powerful tool, and that by strategically concealing and revealing certain features, one can enhance their overall appeal.
Social norms and expectations: The quatrain may also reflect on societal norms and expectations regarding beauty and modesty.

This quatrain is a thought-provoking exploration of the human desire to be seen and admired, while also acknowledging the value of discretion and modesty. It suggests that there is a delicate balance between revealing one's beauty and protecting oneself from unwanted attention.