When did David compose this Mizmor?
Rashi (2): It was when he sent Yo'av and all Yisrael to war in Yerushalayim, and prayed for them - "Tov Ki Sihyeh Lanu me'Ir Lazor" (Shmuel II, 18:3). If not or David, Yo'av would not have been able [to succeed] in war (Sanhedrin 49a).
Radak: He said it when he went out to war. Malbim - it was far from Yerushalayim. David was in danger there. When they heard in Tziyon, they prayed for him, and sent troops to help him. While the troops were going, they heard that David was saved miraculously. When the troops reached there, they defeated the enemy without war, just via Hashem. It seems that the war was with Pelishtim (Shmuel II, Perek 21). David wearied and Yishbi b'Nov wanted to strike him. Avishai ben Tzeruyah helped him strike the Pelishti, and David's men swore "Lo Setzei Od Imanu l'Milchamah" (ibid., 15-18). There was another war in Nov, which they won. David was in great danger (Sanhedrin 95a). The first part of this Mizmor is what they prayed for David (verses 2-4). The second (verses 4-7) is their response when they heard that David was saved, and the third (verses 7-10) is what they said when they defeated the enemy without weapons, only via Hashem.
Why does it say "l'David" with the prefix Lamed?
Radak: It is about David. This is like "Imri Li Achi Hu" (Bereishis 20:13).
