What can the Book of Numbers teaches us today? According to Ron Allen:
Since the Book of Numbers presents the story of the rebellion of the people of Israel in the Desert of Sinai, there is a sense in which the book stands in the middle of the salvation experience of the people of God. The generation that was delivered from slavery in Egypt did not continue to respond to the Lord with faith and gratitude. Instead, they forfeited their part in the Land of Promise. Only their children would experience the blessing of conquest.
Provisionally, we may state that the original recipients of the book were the people of Israel in the second generation from the Exodus, awaiting the command of God to cross the Jordan to conquer the land of Canaan. The book describes the affairs of the people of the first generation, but its teaching is for their children who are now mature and are about to enter Canaan.
We may also venture the purpose of the book in this manner: To compel obedience to Yahweh by members of the new community by reminding them of the wrath of God on their parents because of their breach of covenant; to encourage them to trust in the ongoing promises of their Lord as they follow him into their heritage in Canaan; and to provoke them to the worship of God and to the enjoyment of their salvation. Thus the book that describes the “Desert Years” is designed to encourage spiritual confidence on the part of the people who are about to leave the desert. Despite its sorry record of blemish, betrayal, and benighted living, the Book of Numbers as a whole portrays a confident life of faith in the fear of Yahweh. Further, this confident living, this triumphalism, becomes a major element in the worship of Yahweh.
From “Numbers” in The Expositor’s Bible Commentary, 662-3.