Some groups use these verses to teach that a believer can lose his salvation. But this passage is not actually speaking of the spiritual salvation of individuals. Rather, it concerns Israel as a nation under the Mosaic Law, individual accountability, physical life and physical death. Under the Mosaic Law, if one were obedient to the Law, he would physically live; if one disobeyed the Law, he would physically die. If this passage were speaking about spiritual salvation and spiritual death, then spiritual salvation would be obtained by works. The passage states that “if you do all these things, if you keep all these commandments, then you will live.” Now if the word “living” is spiritual life, spiritual salvation that would mean salvation is by the works of the Law!
Yet the Bible teaches exactly the opposite: no man was ever saved by the works of the Law. Salvation is always by grace through faith plus nothing. Salvation is never by means of works. However, the enjoyment of physical life and the enjoyment of long life under the Mosaic Law was based on the keeping of the Law. If a man was righteous under the Law in that he lived in conformity to the Law, but later in his life disobeyed it, he was deemed punishable under the Law, even to the point of physical death.
Take the case of Moses, who lived most of his life in conformity to God’s righteous standards and was a meek man before the Lord. But one day he disobeyed God and, as a punishment, God said that he, too, would die in the Wilderness Wanderings. He would only get to see the Land, but he would not be able to enter into it. Now, did Moses lose his salvation? No, he did not. But he lost his privilege of being able to die inside the Promised Land and was punished by dying outside the Promised Land. These verses, then, are not referring to individual salvation, but to Israel under the Law. They deal with accountability. They deal with physical life and physical death in connection with keeping the Mosaic Law.
(Fruchtenbaum, MBS 102 “Eternal Security,” 17-18)