The word presumption does not quite mean in Hebrew what it does in English. In English, it simply means "to assume," to take a matter upon oneself without considering all the factors and doing it. However, in the Old Testament, it carries the idea of acting arrogantly—of rebellion. In fact, it means to do something with audacity or to be headstrong. It refers to those who overstep their bounds or dare to act in a disobedient manner. A willfulness is implied in the word that is not contained in English, making it much more forceful.
In other words, a person who sins presumptuously is fully aware of what he is doing; he is fully educated and not in ignorance either of what he is doing or the potential cost of doing it, and he deliberately sets his mind to do it. It is an act of rebellion, an audacious setting one's will, despite all he knows, to go ahead and do it anyway.
By these usages, the word "unintentional" in Leviticus 4 and Numbers 15 can include within it someone who is conscious of what he is doing but does not act audaciously. He does not plan it. He is not rebellious—but weak. God will forgive that, but He will not forgive the sin that is presumptuous according to usage of the word in the Old Testament.
In the New Testament, the word begins very similar to the English usage of the word. It means "to think" or "suppose." Howevver, according to the context in which it is used in the New Testament, it contains the idea of dealing proudly, defiantly, and recklessly. It means to look down upon. A tremendous amount of pride is implied in it.
John W. Ritenbaugh
Examples of Divine Justice
Other Forerunner Commentary entries containing Numbers 15:22: