After assurances that the Lord is with Israel, the Judge/Lord begins to answer concerns that are not stated by Israel. The promise is made that they shall prevail. In particular the Lord promises redress against those who have invaded Israel. It is interesting that the promises are not immediate, however. The promise is that Israel's children will "make haste against thy destroyers." The Lord's promises are with them, but not necessarily immediate.
In the New World, the tensions and difficulties of establishing a colony are very real. This promise to the Lehites is not for ease in their current situation, but for their children. We know that the Old World prophecy of deliverance had periodic fulfillment, and the Nephites had their periodic fulfillment in the New World. The lesson of history is that deliverance once does not mean that we will not lead ourselves into captivity again. The promise is only of the constancy of God's love and care, not our continual protection from harm.