What is the significance of the fact that our ancestors left Egypt "in the month of spring"?
Rashi: Even though we already know that our ancestors left Egypt in Nisan, the Torah is pointing out Hashem's loving-kindness in taking us into the desert in a month that is neither excessively hot nor excessively cold, and in which it does not rain. 1
Ramban (to 13:2) and Seforno: This is why the Torah commands below 2 to ensure that Pesach falls in the spring, 3 by fixing a leap-year when necessary.
Maharal: Refer to 12:2:4.1:1, and to 12:15:3.1:1.
See also Tehilim 68:7 and commentaries. Toras Avigdor (Parshas Bo, citing the Saba of Slabodka) - We should appreciate that we left when it is comfortable to travel. Genuine constant happiness comes through appreciating 'small' things in life that most people take for granted - air, water, sight, ability to walk, shoes ....
See below, "v'Shamarta... l'Mo'adah" (13:11). Refer also to Devarim 16:1:1:1.
Seforno: As it did that year.
