Accidental sin is not so serious as willful sin. God spoke to Moses, Num 15:29-31--"

"You shall have one law for him who does anything unintentionally, for him who is native among the sons of Israel and for the alien who sojourns among them. But the person who does anything defiantly, whether he is native or an alien, that one is blaspheming the LORD; and that person shall be cut off from among his people. Because he has despised the word of the LORD and has broken His commandment, that person shall be completely cut off; his guilt will be on him."

Soon after that a man was found gathering wood on the Sabbath day. He was taken outside the camp and stoned to death by all the people, Num 15:32-36, just as God commanded. God wanted to impress upon His people the seriousness of disobedience of one of the ten commandments. He instructed them to make blue tassels on the corners of their garments, verses 39-40

"It shall be a tassel for you to look at and remember all the commandments of the LORD, so as to do them and not follow after your own heart and your own eyes, after which you played the harlot, so that you may remember to do all My commandments and be holy to your God.”

Some of the people must have thought that killing a man for picking up sticks on the Sabbath was overdoing judgment. Korah gathered some of the leaders and confronted Moses and Aaron, Num 16:3

"You have gone far enough, for all the congregation are holy, every one of them, and the LORD is in their midst; so why do you exalt yourselves above the assembly of the LORD?"

Apparently Korah had a short memory, and did not remember that God had appointed Moses and Aaron to lead His people. Moses announced that God would show who is His. Korah and his followers were invited to take censers and burn incense upon them in the presence of the Lord. Num 16:28-35--

Moses said, "By this you shall know that the LORD has sent me to do all these deeds; for this is not my doing. If these men die the death of all men or if they suffer the fate of all men, then the LORD has not sent me.”
"But if the LORD brings about an entirely new thing and the ground opens its mouth and swallows them up with all that is theirs, and they descend alive into Sheol, then you will understand that these men have spurned the LORD."
As he finished speaking all these words, the ground that was under them split open; and the earth opened its mouth and swallowed them up, and their households, and all the men who belonged to Korah with their possessions. So they and all that belonged to them went down alive to Sheol; -------Fire also came forth from the LORD and consumed the two hundred and fifty men who were offering the incense.”

No other sin is so dangerous as willful rebellion against God. Although we are not under the law of Moses today, these things were written for our instruction, 1 Cor 10:1-12—“

“For I do not want you to be unaware, brethren, that our fathers were all ---- baptized into Moses in the cloud and in the sea; and all ate the same spiritual food; and all drank the same spiritual drink, for they were drinking from a spiritual rock which followed them; and the rock was Christ.”
“Nevertheless, with most of them God was not well-pleased; for they were laid low in the wilderness. Now these things happened as examples for us, so that we would not crave evil things as they also craved.”-------
“Now these things happened to them as an example, and they were written for our instruction, upon whom the ends of the ages have come. Therefore let him who thinks he stands take heed that he does not fall.”
(All scriptures from the New American Standard Updated)

Korah and his followers believed that mankind should be the judge of what is right. Their popular uprising came to a bad end. Today we need to respect the sovereignty and power of God. God has spoken through Jesus, and we are taught to be like Him.