Rashi on Numbers 15:31/רש"י על במדבר ט״ו:ל״א

1דבר ה׳ [BECAUSE HE HATH SCORNED] THE WORD OF THE LORD — The prohibition of idolatry (אנכי and לא יהיה לך) the people heard from the mouth of the Lord but all the other commandments from the mouth of Moses (therefore the prohibition of idolatry is called דבר ה׳ “the utterance of the Lord”) (cf. Sifrei Bamidbar 112:2; Sanhedrin 99a).

2עונה בה [THAT PERSON SHALL UTTERLY BE CUT OFF] HIS INIQUITY IS UPON HIM — only at the time when (under the circumstances that) his iniquity is upon him shall he be cut off, i.e., in the case that he has not repented (Sanhedrin 90b).