Scriptural evidence indicates that the name Michael applied to God's Son before he left heaven to become Jesus Christ and also after his return.
But first it is helpful to understand more about THE Archangel:
The prefix "arch," means "chief" or "principal," (http://www.biblestudytools.com/lexicons/greek/kjv/archaggelos.html)
and implies that there is only ONE Archangel, the chief angel; in the Scriptures. Further implying that there is only one Archangel is that the word "Archangel" is never found in the plural.
So because this evidence demonstrates that there is only ONE Archangel (compare Jude 9, "Michael THE Archangel"), when the voice of the resurrected Lord Jesus Christ is also described as being that of the "Archangel" at 1 Thessalonians 4:16, this suggests that he is, in fact, himself the Archangel.
For much more, see:
Statements by respected trinitarian authorities concerning Christ as being an angel in Rev. 14:14-20
Scholars' Quotes Concerning Jesus as an Angel
"Who Is Michael the Archangel?"
Questions and answers about the Archangel
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