Why does it say that her neck resembles Migdal David?
Rashi: Erect stature is beauty in a woman.
Rashi according to the metaphor: Migdal David is Metzudas Tziyon, the strong fortress. Your neck is Lishkas ha'Gazis, the strength and fortress of Yisrael.
Seforno: Her neck is the general of her army. It is under the head.
Malbim (Melitzah): After describing how the Nefesh itself acts to acquire intellect and Chachmah, now it describes how it conducts the body and rules over it. The intellectual Nefesh is in the skull; Nefesh ha'Chiyunis is in the middle of the body. The neck is the Paroches that divides between them. It is as if the former verbally commands the latter via this curtain. Therefore, the verse depicts the neck as Migdal David, which was built l'Salpiyos. There the Giborim stood bearing bows, to fight the enemies in the gate.
What do we learn from "Tzavarech Banuy l'Salpiyos"?
Torah Temimah citing Brachos 30a: It is the Tel (mound) towards which all Piyos (mouths) turn. (All face the Mikdash when they pray.)
Rashi: It is built for beauty, for all to look at it, to learn its forms and the beauty of its craftsmanship. This is like "Malefenu mi'Bahamos Aretz" (Iyov 35:11. There is no Tov in Malefenu); the Tov in Talpiyos is added, like the Tov in Tarmis and Tavnis.
Why do 1000 shields hang from it?
Rashi #1: The custom of officers is to hang their shields and quivers on the walls of towers.
Rashi #2: Elef ha'Magen is like Magen ha'Elef, based on "Davar Tzivah l'Elef Dor" (Tehilim 105:8) (what guards for 1000 generations).
Malbim (Melitzah): This is a metaphor for fighting enemies of the Nefesh - the troops of old foolish king (Yetzer ha'Ra) who builds fortresses against the small city to conquer it. The Nefesh will rule over him with its Chachmah - "u'Matza Vah Ish Misken Chacham u'Milet Hu Es ha'Ir b'Chachmaso" (Koheles 9:15). The power of arousal has powers to straighten, command and complete. The breasts (mentioned in verse 5) are to straighten and complete; the strong tower in the middle (neck) represents the ruler who commands and rebukes verbally to heed his voice. He forces the power of arousal to submit to the command of the intellect, which stands above it. Elef ha'Magen is the power to straighten.
What are "Shiltei ha'Giborim"?
Rashi: They are quivers in which they put arrows, like "Haveru ha'Chitzim Mile'u ha'Shelatim" (Yirmeyah 51:11). Lishkas ha'Gazis is like this; from there, rulings go out. Torah protects Yisrael.
Rashi according to the metaphor: We find that Talmidim are called arrows and Shelatim - "k'Chitzim b'Yad Gibor Ken Bnei ha'Ne'urim; Ashrei ha'Gever Asher Milei Es Ashpaso Mehem" (Tehilim 127:5-6).
Seforno: They are the shields of the defeated Giborim.
Malbim (Melitzah): This is the power to be Mashlim, and place his rule over them.
