The point of Jude’s example here is this: The false teachers believed that salvation has freed man from any law at all. They believed the angels were jealous since humankind was created a little lower than the angels and yet received such grace from God as evidenced in salvation. They then slandered the angels by saying that the angels gave the law out of envy and ill-will. Michael, however, did not accuse the devil back, but merely appealed to the Lord’s judgment.
The point for Jude’s readers is that if Moses and Michael did not have the authority to answer the slanders of Satan, but instead appealed to the Lord to judge between them, then we cannot reject the law on our own authority. Even if you were as righteous as Moses and Michael, you still are not above being accused under the law and are under the Lord’s authority through his Law.
Michael’s statement, “The Lord rebuke you!” leaves the final judgment to the Lord. It is in a legal context that this quote has its origins. In Zech. 3:2 Satan stands at the side of the High Priest Joshua to accuse him and the Lord himself utters these words. This is in line with what Jude is doing in this epistle. Jude is not condemning the false teachers on his own authority, but speaking the truth and warning them in light of the coming day of the Lord’s judgment (Jude 14-15). That all judgment has been committed to the Son is important since he had authority over Satan during his earthly ministry and will have authority in the Day of Judgment.