Every sin must be punished.
Sin is unrighteousness. That is, to behave in a way which is inconsistent with GOD's intended design.
GOD's just-ness requires that every unrighteous action is punished.
When GOD sets a boundary, He makes that boundary clear and anyone who crosses it, intentionally or unintentionally becomes guilty of sin.
For instance, in the Garden of Eden, Eve and Adam crossed the boundary of touching and eating the forbidden fruit. GOD kicked them out of the garden and cursed the land because of their sin, cursed Eve with painful child labor, and subjected them to physical death. This was not GOD's fault. It was man's.
The clearest illustrations of this principle that all sin must be punished can be seen within GOD's relationship with His own chosen nation, Israel.
From the time GOD called Israel out of Egypt, at Mount Sinai, when He was giving Moses the Law, GOD sternly warned Israel regarding the severity of punishment for disobeying Him:
4 “You shall not make for yourself an idol or a likeness of anything in heaven above, or in the earth beneath, or in the waters under the earth. 5 You shall not bow down to them or serve them, for I, the Lord your God, am a jealous God, recompensing the sins of the fathers on the children to the third and fourth generation of those who hate Me; 6 but showing mercy to thousands, to those who love Me and keep My commandments.
(Exodus 20:4-6 OSB)
This principle is repeated multiple times in the Law.
The Law of Moses included severe punishment for the rebellious sinner, often including stoning outside the camp. Here are a few rapid-fire examples from Leviticus 20:
7 Therefore, you shall be holy, for I the Lord your God am holy. 8 You shall keep My ordinances and perform them: I am the Lord who sanctifies you. 9 Whatever man curses his father or mother shall surely be put to death. He cursed his father or mother. Thus he shall be guilty.
10‘The man who commits adultery with another man's wife, or who commits adultery with his neighbor's wife, the adulterer and the adulteress shall be put to death. 11 The man who lies with his father's wife has uncovered his father's nakedness; both shall surely be put to death, for they are guilty. 12 If a man lies with his daughter-in-law, both shall surely be put to death. They are impious, and therefore guilty. 13 If a man lies with a male as he lies with a woman, both committed an abomination. They shall be put to death, for they are guilty. 14 If a man marries a woman and her mother, it is wickedness. They shall be burned with fire, both he and they, that there may be no wickedness among you.
(Leviticus 20:7-14 OSB)
Though GOD loved Israel deeply, He foreknew that the majority of them would rebel and foresake Him. For this reason, GOD had Moses deliver one final speech to Isreal before his death, in the form of a song known as the Song of Moses. It begins as follows:
1 “Take heed, O heaven, and I will speak;
And let the earth hear the words of my mouth.
2 Let my proverbial saying be awaited as the rain,
And let my words come down
As raindrops on the wild grass,
And as snow fall on the sown grass.
3 For I invoke the Lord's name:
Ascribe greatness to our God.
4 He is God, His works are true;
And all His ways are judgment,
A faithful God and without injustice;
Righteous and holy is the Lord.
5 “They sinned; the blameworthy children are not His,
A generation twisted and perverse.
6 Is this how you repay the Lord,
O foolish and unwise people?
Is He not your Father, who acquired you?
Has He not made and created you?
41 ... I will render vengeance on My enemies,
And repay those who hate Me.
42 I will make My arrows drunk from blood;
And My sword shall devour flesh
From the blood of the slain and the captives,
From the heads of the leaders of the enemy.”’
43 “Rejoice, O Heavens, together with Him,
And worship Him, all the sons of God;
Rejoice, O Gentiles, with His people;
And let all the angels of God be strong with Him;
For He will avenge the blood of His sons
And render vengeance to His adversaries;
And the Lord will purify His people's land.”
(Deuteronomy 32:1-6, 41b-43 OSB)
Centuries later, in the time of fulfillment of the Song of Moses, the apostle Paul warned the Corinthian Christians of the severity of GOD's punishment for sin and the danger of turning away from Him:
1 For I do not want you to be ignorant of the fact, brothers and sisters, that our ancestors were all under the cloud and that they all passed through the sea. 2 They were all baptized into Moses in the cloud and in the sea. 3 They all ate the same spiritual food 4 and drank the same spiritual drink; for they drank from the spiritual rock that accompanied them, and that rock was Christ. 5 Nevertheless, God was not pleased with most of them; their bodies were scattered in the wilderness.
6 Now these things occurred as examples to keep us from setting our hearts on evil things as they did. 7 Do not be idolaters, as some of them were; as it is written: “The people sat down to eat and drink and got up to indulge in revelry.” 8 We should not commit sexual immorality, as some of them did—and in one day twenty-three thousand of them died. 9 We should not test Christ, as some of them did—and were killed by snakes. 10 And do not grumble, as some of them did—and were killed by the destroying angel.
11 These things happened to them as examples and were written down as warnings for us, on whom the culmination of the ages has come. 12 So, if you think you are standing firm, be careful that you don’t fall!
(1 Corinthians 10:1-12 NIV)
There are perhaps no clearer words from GOD regarding the punishment of sin than these from Ezekiel:
4 For all souls are Mine; the soul of the father as well as the soul of the son is Mine.
“The soul who sins, he shall die. 5 But the man who is righteous and does judgment and righteousness, 6who will not eat on the mountains, or lift up his eyes to the inventions of the house of Israel, or defile his neighbor's wife, and who will not approach a woman during her menstruation, 7 or oppress any man, but who will restore to the debtor his pledge, and commit no robbery, but who will give his bread to the hungry and cover the naked, 8 and who will not lend his money with interest, but will turn his hand from wrongdoing, and do righteous judgment between a man and his neighbor, 9 and walk in My ordinances, and keep My requirements to do them—this man is righteous. He will surely live!” says the Lord.
20 But the soul who sins shall die. The son shall not bear the wrongdoing of his father, nor shall the father bear the wrongdoing of his son. The righteousness of a righteous man shall be upon himself, and the lawlessness of a lawless man shall be upon himself. 21 But if a lawless man turns from all the lawless deeds he commits, keeps all My commandments, does righteousness and shows mercy, he will surely live and not die. 22 None of the transgressions he commits will be remembered. In the righteousness he does, he shall live. 23 Do I ever will the death of a lawless man,” says the Lord, “since My will is for him to turn from the evil way and live?
26 When the righteous man turns away from his righteousness, commits a transgression, and dies in the transgression he commits, he should die because of it. 27 Again when a lawless man turns away from the lawlessness he commits and does judgment and righteousness, then he guards his life; 28 for he turned himself away from all the ungodliness he committed. He will surely live and not die.
(Ezekiel 18:4-9, 20-23, 26-28 OSB)