What is the significance of the fact that the people were stricken with a Divine terror?
Seforno: The threat that the surrounding nations would attack them when they left Shechem was real, and it was only due to Hashem's intervention that it did not happen. 1
Targum Yonasan: They left the vicinity of Shechem 'thanking Hashem and praying,' to which Hashem responded by terrifying the surrounding nations into refraining from attacking them. 2
Ohr ha'Chayim #1: Normally, when one flees, others realize that he is afraid; even so, the other nations feared Yaakov.
Ohr ha'Chayim #2: Normally, when [an attacker] goes away, the victim pursues him (this is his only chance)! Even so, they did not pursue Yaakov.
Malbim: Fear of Hashem fell on the surrounding cities. They believed that two [youths] were able to kill an entire city due to Divine help; it was Hashem's punishment for their extortion. Also, since Yaakov's sons prepared their hearts to Hashem, their Yir'as Hashem spread to the cities.
Ha'amek Davar: They did not yet merit the sword of Avraham, nor the Shalom of Yaakov, for they did not pray yet. In any case, Hashem guarded them. This is a Siman l'Banim - fear of Shamayim falls on the nations not to wipe out Yisrael. Hashem is Nora - if not for his fear, one nation could not survive among... (Yoma 69b).
Particularly as Yaakov pointed out to his sons, "and they will gather against me and smite me ... !" (See above, Bereishis 34:30).
The Ramban (to 34:13), based on the Sefer Milchamos Bnei Yaakov (Sefer ha'Yashar), explains that three battles did in fact, take place, and, despite Yaakov's participation (See Rashi to 48:22) it was only due to a miracle that they emerged without losing a man (as the Torah states in 35:6). And the terror that Hashem cast into their hearts prevented the nations from joining forces and falling upon them as numerous as the sand by the sea-shore. The Ramban also comments that the Torah does not record these battles, since, due to the immense strength of Yaakov and his sons, the miracles involved were hidden miracles, which the Torah tends not to record.
