In Lev. 6 the trespass committed against the Lord, has its immediate expression in a man's own want of righteousness and grace towards his neighbor. His act was, chewing what he himself was: though against the Lord, still it was unto his neighbor: the immediate question was between him and his neighbor, yet against the Lord, but mercy for him, as in Psa. 51:44Against thee, thee only, have I sinned, and done this evil in thy sight: that thou mightest be justified when thou speakest, and be clear when thou judgest. (Psalm 51:4): so with Paul, the blasphemer, persecutor and injurious, it was ignorantly in unbelief: it assumed not in his conscience the direct rejection of the grace of God.
In Num. 15 the presumptuous sin is not in ignorance, nor to a neighbor, but reproaching the Lord, despising the word of the Lord. In the beginning of the chapter, the Lord revealed what was a sweet savor unto Him, in an offering made by fire: this could not be deviated from: there was one ordinance for them of the congregation, and ALSO for the stranger: and this an ordinance forever. One law and one manner shall be for you and for the stranger that sojourneth with you (verses 15, 16).
It is a solemn thing to offer a sweet savor unto God: the savor of Christ is sweet unto him: God can have no delight in anything where the savor of Christ's name is not: be it what it may, it is sin either ignorantly done, and remedy in mercy opened up, or, with high hand, the Lord reproached and His word despised.