Jude 1:9 Yet Michael the archangel, when contending with the devil he disputed about the body of Moses, durst not bring against him a railing accusation, but said, The Lord rebuke thee.
Jude is quoting from Zechariah 3.
Zechariah 3:2 And the LORD said unto Satan, The LORD rebuke thee, O Satan; even the LORD that hath chosen Jerusalem rebuke thee: is not this a brand plucked out of the fire?
Those who are baptised into Christ are described as his body.
Ephesians 5:30 For we are members of his body, of his flesh, and of his bones.
Israel were baptised into Moses
1 Corinthians 10:2 And were all baptized unto Moses in the cloud and in the sea;
In this way Israel became the ‘body of Moses’. Therefore ‘body of Moses’ in Zechariah refers to the congregation of Israel which had returned from Babylon. In this sense, they represented a ‘brand plucked out of the fire’. The Satan or adversary were the people of the land who attempted to prevent the rebuilding begun by Zerubbabel and Joshua.
Ezra 4:4 Then the people of the land weakened the hands of the people of Judah, and troubled them in building, 5 And hired counsellors against them, to frustrate their purpose, all the days of Cyrus king of Persia, even until the reign of Darius king of Persia.
The rebuke finally came in the decree of Darius.
Ezra 6:6-12 Now therefore, Tatnai, governor beyond the river, Shetharboznai, and your companions the Apharsachites, which are beyond the river, be ye far from thence: 7 Let the work of this house of God alone; let the governor of the Jews and the elders of the Jews build this house of God in his place. 8 Moreover I make a decree what ye shall do to the elders of these Jews for the building of this house of God: that of the king’s goods, even of the tribute beyond the river, forthwith expenses be given unto these men, that they be not hindered. 9 And that which they have need of, both young bullocks, and rams, and lambs, for the burnt offerings of the God of heaven, wheat, salt, wine, and oil, according to the appointment of the priests which are at Jerusalem, let it be given them day by day without fail: 10 That they may offer sacrifices of sweet savours unto the God of heaven, and pray for the life of the king, and of his sons. 11 Also I have made a decree, that whosoever shall alter this word, let timber be pulled down from his house, and being set up, let him be hanged thereon; and let his house be made a dunghill for this. 12 And the God that hath caused his name to dwell there destroy all kings and people, that shall put to their hand to alter and to destroy this house of God which is at Jerusalem. I Darius have made a decree; let it be done with speed.
In conclusion, I believe ‘the body of Moses’ does refer to the congregation of Israel who went back to the land with Ezra, Zerubbabel and Joshua.
I hope you find this helpful.