The events recorded in Numbers 13-14 take place in the middle of year 2 of Israel's time in the wilderness. By chapter 20, we are at the beginning of year 40. Only a handful of events from the intervening years are described in the biblical narrative.
One is the episode of the "Sabbath gatherer" described briefly in Numbers 15:32-36. The wording and placement of this incident in the text can help us learn some lessons from it.
First, note that those who confronted the man for his sin "brought him to Moses and Aaron and to all the congregation," wording similar to Numbers 13:26, where the leaders who had visited the land brought back their report. The similarity in wording invites us to compare Israel's responses to the two incidents.
In Numbers 13-14, Israelites are led astray by the bad report of ten of the leaders. Many would like to return to Egypt, rejecting God's deliverance and his covenant. Some call for Moses to be stoned to death and replaced by a new leader.
On the other hand, the Israelites in Numbers 15 seem to have learned a lesson. Instead of turning against Moses, they are zealous for the teachings of Moses. Instead of being led astray by sinners, they root sin out of their midst. Instead of calling for the stoning of Moses, they stone the violator.
Second, this incident is mentioned in Numbers 15 immediately after a warning about defiant sins, suggesting that the man's sin fell into that category. The word for "gathering" in Numbers 15:32, qasas, is an uncommon one in the Bible, appearing elsewhere in the Torah only in Exodus 5:7, 12. The verses in Exodus are about Israelite slaves in Egypt being forced to gather straw to make bricks. The similarity in wording invites us to compare the gatherer's activity with that of the earlier slaves.
The Sabbath commandment that the gatherer was violating is an important sign of the covenant (Ex 31). By openly gathering instead of resting on the Sabbath, the man was showing, in effect, that he preferred slavery in Egypt to being in covenant with the God who had delivered him from Egypt. And since the Sabbath also pointed forward to a coming spiritual rest in the land (Heb 4), the man's actions implied a rejection of the land and that future rest. These things help explain why the man was executed. He was not someone who had slipped up and accidentally violated the Sabbath. Instead, he was someone who was rejecting God and opting out of his covenant and Israel's divine calling.
Third, the placement of the incident shortly after Numbers 13-14 suggests that the gatherer be seen as a representative of the older generation of Israelites who refused to enter the Promised Land. In contrast, the younger generation was more anxious to get there.
We can illustrate this contrast with a Jewish tradition about the unnamed gatherer. It was suggested by Rabbi Akiva that the man was Zelophehad, one of the older generation who had "died for his own sin" in the wilderness (Nu 27:3). His daughters, part of the younger generation of Israelites, were eager to inherit property in the Promised Land.