Sforno on Exodus 4:14/ספורנו על שמות ד׳:י״ד

1הלא אהרן אחיך? If it had been My intention to appoint someone naturally suited for the task, there is your brother Aaron, the Levite, undoubtedly a wise man as are all his brothers the Levites.

2כי ידעתיו כי דבר ידבר הוא, for I am well aware that he is an excellent speaker without needing training, וגם הנה הוא יוצא לקראתך וראך ושמח בלבו, and although he is on the way to meet you out of respect for you and your elevation to an even higher status than his own, he will undoubtedly be happy to serve as your interpreter full-heartedly.