sin of presumption

But if a man come presumptuously upon his neighbor, to slay him with guile; thou shalt take him from mine altar, that he may die. Exodus 21:14

If a man wanted mercy, he would grab the horns of the altar. In this case, someone murders another with premeditation thinking "I can get away with this if I grab the horns of the altar". God says to remove him from the altar and kill him, he gets no mercy.

This is no different than someone thinking "I can get away with this sin, as long as I ask forgiveness afterwards".

Contrast premeditated, arrogant rebellion with someone who is not acting in rebellion but instead out of weakness, mistakenly, unintentional, or in ignorance... It is no less a sin, but mercy can be accorded in this case...

Speak unto the children of Israel, saying, If a soul shall sin through ignorance against any of the commandments of the LORD concerning things which ought not to be done, and shall do against any of them Leviticus 4:2

Who can understand his errors? cleanse thou me from secret faults. Psalm 19:12

There is no offering or sacrifice for the presumptuous, willful sin:

But the soul that doeth ought presumptuously, whether he be born in the land, or a stranger, the same reproacheth the LORD; and that soul shall be cut off from among his people. Because he hath despised the word of the LORD, and hath broken his commandment, that soul shall utterly be cut off; his iniquity shall be upon him. Numbers 15:30-40

Therefore by the deeds of the law there shall no flesh be justified in his sight: for by the law is the knowledge of sin. Romans 3:20

Keep back thy servant also from presumptuous sins; let them not have dominion over me: then shall I be upright, and I shall be innocent from the great transgression. Psalm 19:13