Moshe teaches the people that their achievement of true fear of God will allow them to not fear any enemy.
The following article is reprinted with permission from the Orthodox Union.
In preparing the Children of Israel for the conquest of the land of Canaan, Moshe anticipates the people's trepidation, and he promises Hashem's ongoing support:
Perhaps you might say in your heart, "These nations are more numerous than I; how can I dispossess them?" You shall not be afraid (lo tira) of them. You shall surely remember that which Hashem, your God, did to Pharaoh and to all of Egypt: The great tests which your eyes saw, and the signs and the wonders, and the strong hand, and the outstretched arm whereby Hashem, your God, brought you out--so will Hashem, your God, do to all the nations before whom you are afraid (yarei). Furthermore, Hashem, your God, will release the hornet against them, until the destruction of those who are left and those who hide themselves before you. You shall not be intimidated/frightened (lo ta'arotz) before them, because (ki) Hashem, your God, is in your midst, a God Who is mighty and feared (nora) (Devarim 7:17-21).
Moshe is trying to assure the people that they have no reason to fear the inhabitants of the land in the upcoming wars, because Hashem will defend them just as He did in Egypt. So, why is He described as "a God Who is mighty and feared?" Would it not have been more comforting to hear that Hashem is caring and protective?
Haketav V'hakabbalah (R. Yaakov Tzvi Meklenburg, 1785-1865), quoting Rabbi Yehudah Leib Margaliot (1747-1811), head of the bet din (rabbinic court) in his birthplace Lesslau, explains that fear of Hashem is different from any other feeling we have towards Him. For example, one may fully honor, love and be grateful to other people, with no diminution of the honor, love and gratitude that are due to Hashem. This is not, however, the case when it comes to fear of Hashem, which is lessened by the fear of others, as we shall elucidate.
(Of course, the Torah teaches us to revere our parents and our teachers, and it uses the same word, yir'ah, for both. However, these are forms of reverence that are commanded precisely because they develop one's fear of Heaven; they certainly do not compete with it.)
The idea of the preeminence of the fear of Hashem is demonstrated in the exchange cited in the Talmud (Berachot 28b) between Rabbi Yochanan ben-Zakkai and his students while the sage lay on his deathbed. The students asked their teacher to bless them, and his blessing was: "May it be His will, that your fear of Heaven be as much as your fear of flesh-and-blood." And when his students asked, "No more than that?" he replied, "Would that it were as much as that! For you know that when a person is about to sin, he first thinks, 'I hope no person sees me.' One's awe of Hashem must supersede all else."