Musar zu Schir haSchirim 5:13

We have now learned that the three parts of the Tabernacle correspond to the three parts of the universe concerning which King David said in Psalms 103,20: "Bless the Lord, O, His angels, mighty creatures who do His bidding, ever obedient to His bidding. Bless the Lord all His hosts, His servants who do His will; bless the Lord all His works, through the length and breadth of His realm." David's son Solomon also adopted his father's outlook when he alluded to this in three consecutive verses in Song of Songs 5,13-15. Three different parts of the human body form the subject of those verses, each one representing a different aspect of the universe and how man's composition reflects this division of the universe into three constituent parts. I (Rabbenu Bachyah) have explained this in detail when I discussed Jacob's dream of the ladder." Thus far the quotation from Rabbenu Bachyah.

It would seem that the Torah compares other hairs to forces originating in the emanation דין, for we read in Song of Songs 5,13: לחייו כערוגת הבשם, "His cheeks are like a bed of spices," מגדלות מרקחים, "towers of perfume;" שפשותיו שושנים, "his lips are like lilies," נוטפות מור עבר, "they drip flowing myrrh." We also have a verse in Song of Songs 4,3: כחוט השני שפשותיך, "Your lips are like crimson thread." All the areas of the body mentioned in those verses are allusions to the attribute of Justice. Rabbi Elazar, in his book called ספר הנפש, writes that the hairs on one's head derive their nourishment from the brain, similar to מלאכי הכבוד, a category of angels; he goes into a great deal of detail on the subject.