What does this Mizmor discuss?
Malbim: It is about David's wars with Aram Naharayim, Aram Tzovah and Edom, together (Shmuel II, Perek 8). It seems that first the enemies breached cities of Yisrael and took captives from Shechem and Emek Sukos. This aroused Gil'ad and Menasheh in Ever ha'Yarden, who were close to Har Efrayim, to help Efrayim (Shechem is only Efrayim's border); they defeated the enemies.
Why does it say "l'David Michtam"?
Rashi #1: This is like "Kesem Paz" (Shir ha'Shirim 5:11), something treasured.
Rashi (from Tanchuma Devarim 3): He conducted himself like one who is Mach (poor) and Tam (simple), even when he was king.
Refer to 16:1:2:1-4 and the notes there.
Why does it say "Al Shushan Edus"?
Rashi: It is due to the testimony of the Sanhedrin 1 , which is compared to Shoshanim (roses) - "Sharerech Agan ha'Sahar... Sugah ba'Shoshanim" (Shir ha'Shirim 7:3). When David sent Yo'av to fight Aram Naharayim, they told him, you descend from Yakov, who swore to Lavan "Ed ha'Gal ha'Zeh" (Bereishis 31:52)! David asked the Sanhedrin. They answered, Aram transgressed first - "Min Aram Yancheni Valak" (Bamidbar 23:7). Also, Kushan Rish'asayim (who subjugated Yisrael in the days of the Shoftim - Shoftim 3:8) was from Aram 2 .
Why does it say "Lelamed"?
Radak (2): Hashem gave Torah to Yisrael to teach to an answer to all nations. Refer to 60:1:3:1.
