Or HaChaim on Numbers 14:23/אור החיים על במדבר י״ד:כ״ג

1 אם יראו…וכל מנאצי, "Surely they shall not see….any of those who have spurned Me." Why did G'd have to especially mention the people who had spurned Him? Who would have dreamt that those people would be exempt from this retribution? Perhaps they had to be mentioned seeing that G'd had spoken of a people who had tested Him already on ten different occasions. We might have thought that all those who had not been guilty ten times, such as the people who had not yet been 20 years of age at the Exodus, would have been exempt from this oath that they would die in the desert. G'd therefore made it clear that even these young people were included as they had spurned G'd on this occasion. The people described here as having spurned G'd are the ten spies as well as the people who had thrown stones at the cloud behind which Joshua and Caleb had taken cover (compare Sotah 35).

2Our verse may also have introduced a new dimension of punishment of the spies. Seeing they were not worthy of the land, they had forfeited their share in it. This is why we are told in Baba Batra 117 that the descendants of the spies did not take part in the distribution of the land under Joshua. They received shares based only on the size of the families of their grandfathers. The remainder of the generation who were now slated to die in the desert received their share of the Holy Land based on their present family status, i.e. how many male children they had. The verse ends with the promise that "My servant Caleb as well as his descendants will inherit their shares in the land."