“But if you sin unintentionally, and do not observe all these commandments that the LORD has spoken to Moses, all that the LORD has commanded you by Moses, from the day that the LORD gave commandment, and onward throughout your generations, then if it was done unintentionally without the knowledge of the congregation, all the congregation shall offer one bull from the herd for a burnt offering, a pleasing aroma to the LORD, with its grain offering and its drink offering, according to the rule, and one male goat for a sin offering. And the priest shall make atonement for all the congregation of the people of Israel, and they shall be forgiven, because it was a mistake, and they have brought their offering, a food offering to the LORD, and their sin offering before the LORD for their mistake. And all the congregation of the people of Israel shall be forgiven, and the stranger who sojourns among them, because the whole population was involved in the mistake.
“If one person sins unintentionally, he shall offer a female goat a year old for a sin offering. And the priest shall make atonement before the LORD for the person who makes a mistake, when he sins unintentionally, to make atonement for him, and he shall be forgiven. You shall have one law for him who does anything unintentionally, for him who is native among the people of Israel and for the stranger who sojourns among them. But the person who does anything with a high hand, whether he is native or a sojourner, reviles 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 utterly cut off; his iniquity shall be on him.” (Numbers 15:22-31 ESV)
There is sacrifice for only one kind of sin, and that is sin done without a “high hand,” that is, sin done without a hand of rebellion held up against Yahweh in deliberate despising of His authority. Sins done unintentionally are those done in ignorance or at least with a giving in to weakness. These kind of sins can be forgiven through offering of a sacrifice. High handed sins will be punished by God if undiscovered by the community, or punished by the community if discovered, and death will be the penalty.
In Hebrews 10:26-31 that author equates purposely leaving the faith and denying the gospel as such a deliberate sin for which there is no forgiveness. It is someone who knows the power of the gospel and its truthfulness but who argues that it is false. A true believer would never do that. One who has been born again will persevere in faith. Those who sin deliberately by leaving the truth signal that they were not saved to begin with.
We can perhaps see the difference between these two sins in Jesus’ parable of the prodigal son. The prodigal yearns for freedom and adventure and leaves with his father’s inheritance, shameful to say the least, and spends it in profligacy, only then to realize what a fool he has been and how much his father loves him and is good, so he returns. His older brother, on the other hand, despises his father and resents his forgiveness of his brother and refuses to come to the party. Both treat the father shamefully, but the one does so from a heart that really loves and respects his dad, the other from a heart that is alienated from his dad and seeks to justify himself and his hurt at the father’s expense.
Israel had just sinned with a high hand, refusing to trust and obey God and attack Canaan in God’s power. That generation must die and over the next 40 years does so.