Please explain Jude 9 about Michael contending with the devil about the body of Moses. Why would a biblical writer refer to something that is not in the Bible?
The account of Michael contending with the devil is found in one of the ancient pseudepigraphal books. The word pseudepigrapha means “falsely-inscribed.” A collection of ancient writings was given this name because they were written under the falsely-assumed authorship of long-deceased Old Testament saints to give them an air of authority and importance. It would be like Larry Spargimino writing a Q&A column and signing George Washington’s name to it.
According to some early Christian writers—Clement of Alexandria, Didymus of Alexandria, and Origen—Jude is referring to an incident recorded in The Assumption of Moses. We have to take their word for it because only small fragments of these pseudepigraphal writings have survived. Jude 14–15 quote 1 Enoch, another non-biblical writing.
Jude is not the only biblical author to quote from non-canonical writings. The Apostle Paul quotes from Aratus (Acts 17:28), Menander (1 Corinthians 15:33), and Epimenides (Titus 1:12). These references to non-biblical works do not indicate that Paul and Jude considered them as “Scripture,” but that the biblical authors found the statements to be helpful for the purpose of illustration and clarification.
In verse 9, Jude is writing against the false teachers who, with great arrogance and ignorance, speak of things about which they know nothing. In verse 8, we are told that they “despise dominion,” meaning that they reject authority. “These filthy dreamers speak evil of dignities.” Literally, they speak evil of “glories.”
Some think that this is a reference to angelic beings, who are glorious in their celestial roles. Just as the men of Sodom insulted angels, these false teachers of whom Jude speaks scoff at all authority. Others believe that “dignities” might be a reference to church leaders, for Hebrews 13:17 refers to their authority.
Whichever interpretation one takes, the point is the same. Even Michael the archangel, when disputing with the devil about the body of Moses, did not accuse him but rather looked to the Lord’s authority and said: “The Lord rebuke thee.” Jude is illustrating the dangerous impropriety of speaking evil of exalted beings.
“But why,” we might ask, “would the devil want the body of Moses?” While the Bible does not give much light on this, there are several possibilities. In his book Angels: An Historical and Prophetic Study, pp. 53–54, Dr. Bob Glaze states that Satan could have used the body of Moses against the Israelites who, when seeing the body of Moses, would begin to question the Lord’s grace and mercy to them. It would have been a devastating blow to their confidence in God.