Exodus 4:14

(14) The Levite.—Aben-Ezra and Rosenmüller think that this was the usual designation of the brother of Moses among the Israelites, who thus distinguished him from other Aarons. But as a distinguishing mark, the term would be superfluous here, since “thy brother” prevented the possibility of any other Aaron being thought of. Probably, the term is a title of honour, the priestly character already attaching to the tribe in God’s counsels.

I know that he can speak well.—Heb., I know that speaking he can speak. Facility of utterance, rather than excellence of speech, is intended.

And also, i.e., not only does his ready speech make him a suitable person to appoint, but he is coming to join thee, so that he and thou may arrange your respective parts at once.