The source of physical beauty of a woman:
The beauty of a woman derives from the Sefira of Tiferes. It is a sign and omen of the Divine beauty found above in Atzilus. When a spark of the beauty of Tiferes of Atzilus resides on a person, it becomes expressed in the person’s physical beauty and appearance. One who sees this beauty is not allowed to attach himself to it, but rather to the beauty of Tiferes of Atzilus. This is why Hashem occasionally suddenly shows a person a woman of beauty, as a message for him to attach himself to the Divine beauty of Hashem. On this Shlomo Hamelech states “Tzena Uriena Bnos Tziyon” which means that when one sees Bnos, the beauty of a woman, who should Tzena, leave the physical boundaries and look up to its source in Tiferes of Atzilus, as Tziyon, the physical beauty is a mere sign of the beauty found above.
 Torah Or [Maggid] 18-19