Komentaryo sa Mga Bilang 15:30: Rashi, Sforno, Or HaChaim & Rashbam

ביד רמה [BUT A PERSON THAT DOETH OUGHT] WITH A HIGH HAND — i.e. with premeditation.

את ה' הוא מגדף, there is never any atonement for this even if there is complete remorse which is due to the fear of the punishment in store. Only the death of the guilty person can lead to his atonement. This was also the reason why the repentance of the Israelites for the sin of the spies could not be atoned for during their lifetime, although the repentance itself has been documented by the Torah in Deuteronomy 1,45.

והנפש אשר תעשה ביד רמה, But the person who acts defiantly, etc. This means that if someone deliberately worships idols, G'd considers it as if he had blasphemed against Him. This is why his punishment is that he will be cut off from amongst his people.

מגדף is synonymous with מחרף HE REVILETH, as in (Ezekiel 5:15) “it shall be a reproach (חרפה) and a reviling (גדופה) (Isaiah 37:6) “the servants of the king of Assyria have reviled (גדפו)”. Further, our Rabbis derived from here the law that he who blasphemes the name of the Lord is liable to excision (Keritot 7b).