This title is a quote from Moses’ words in Deuteronomy 7:21. That is significant because in that chapter, Moses drew out the Lord’s mercy in making a minor people his treasured possession (Deuteronomy 7:6–7), and then stressing how this God will prosper this trivial nation and make them great (Deuteronomy 7:12–16). They should remember what God did to Pharaoh, the signs and wonders, the mighty hand and outstretched arm their fathers had witnessed so that they never fear their adversaries (Deuteronomy 7:17–20). In that context Moses says, You shall not be in dread of them, for the Lord your God is in your midst, a great and awesome God
(Deuteronomy 7:21). With his reference to this chapter, Nehemiah is recalling for his own benefit and consciously calling to God’s mind God’s own promise that no one shall be able to stand against you
(Deuteronomy 7:24). Of course, those who heard (or read) his prayer would also be reminded of God’s own promise.
5 And I said, “O LORD God of heaven, the great and awesome God who keeps covenant and steadfast love with those who love him and keep his commandments,