ANSWER: First, let us look into a little background on who is the Archangel Michael. His name means "who is like God" and is Strong's Concordance #4317 for its use in the Old Testament. He is referred to in Daniel 10 as "one of the chief princes" in verse 13 of the chapter. In the thirteenth chapter of Daniel, the archangel has the title 'great prince.' He is also mentioned in the book of Revelation as the being leading the angelic hosts against the devil and his demons (Revelation 12:7 - 8).
Archangels are spirit beings who are at God's service and endowed with tremendous power and knowledge. Interestingly, the Bible only reveals the names of only two of these types of angels: Michael and Gabriel. The only other angel mentioned by name in the Bible, Lucifer (who became the devil), was not one of them.
The Bible verse you have questions about is located at Jude 1:9.
9. But Michael the archangel, when he was personally taking issue with the devil, disputing about the body of Moses, did not presume to pronounce a reviling judgment against him . . . (Jude 1:9)
There exists a variety of interpretations in Biblical commentaries regarding this event. Many of them SEEM, on the surface, to be correct. On closer inspection, however, they are found to be completely false. For example, one commentary assumes God needed Moses' body in order to resurrect him sometime before he appeared in the Transfiguration of Jesus. In this scenario, the devil is arguing that his body should be left in the ground in an effort to somehow thwart God's plans. This argument is groundless since NO ONE, not Moses, Elijah, King David and so on, has yet to be resurrected from the dead or has gone to heaven except Christ (see our article on the First Resurrection).
Now, in answer to your question, the first commandment states that we are to have no other gods before the true God (Exodus 20:1 - 3). Satan would have made the body of Moses and his grave an object of worship, just as he does with so many things in this world. Israel had formally been guilty of worshipping the golden calf, and the body and tomb of Moses, the revered leader of the nation, would have been a constant place of visit by the people of Israel, had they known the location of his body. People today do similar things, such as Russia having a public tomb for Stalin and Lenin. Many countries like the United States have a tomb for the 'unknown soldier,' and so on where people go today and dwell on the past.
Memorials force us to dwell in the past, rather than dwelling in the present and going on with our lives. Some people worship these types of memorials as icons. God wants our worship to be only of Him, instead of some shrine to remind us of the past. Satan will use anything he can, even the body of Moses, to try and direct the focus of human minds away from God and onto something that is physical and temporary. Thank you for your question.