The hidden interpretations or allegories of this chapter are readily apparent. Manna, which in Hebrew means “prepared” or “a gift,” since it is prepared and given without our hands, denotes the Gospel of God, just as Christ also explains John 6:32: “Moses did not give you bread from heaven, but My Father gives you the true bread from heaven.” For this heavenly Word is not given to the world by reason of our powers or merits. The want and affliction in the desert for forty years denote the misery of conscience struggling in sin, where there is hunger and thirst; then the fiery serpents and scorpions, that is, the bite and sting of sin, which afflicts us dreadfully. Manna comes and feeds us, and the stream comes from the struck rock; that is, the Spirit is gained for us through the crucified Christ, and He refreshes us, so that we shall never thirst (John 4:14). Furthermore: As unreasonable as it was that waters should flow from a struck rock, so unthinkable it is that the Spirit of life should come from the death of Christ. Even Moses fell here. For who would hope for a life-giving Spirit from dead and buried flesh?
The abundance and the happiness in the Land of Promise are the riches of the gifts of the Spirit, the treasures of wisdom and knowledge given us in Christ, where we dwell safely and richly in every blessing of heaven (1 Cor. 1:4–5). Here it is necessary that we be not putted up as though we were satiated, but that we gratefully bless God, who has given all these things to those who were not only undeserving but even cursed and lost under the poverty of sin. This is enough or this time.
Luther’s works, vol. 9: Lectures on Deuteronomy 1525