Identifying the Impediment
The three verses of Shemot 4:10, 6:12, and 6:30 describe Moshe's speech difficulties using the terms of "לֹא אִישׁ דְּבָרִים", "כְבַד פֶּה וּכְבַד לָשׁוֹן" and "עֲרַל שְׂפָתָיִם".1 Exegetes discuss the meaning of these expressions,2 debating whether these terms all refer to the same condition, and whether or not Moshe's disability was of a physical nature.
Temporary or Permanent?
Contributing to the mysterious nature of the disability is Moshe's enigmatic statement at the Burning Bush that his condition has affected him "גַּם מִתְּמוֹל גַּם מִשִּׁלְשֹׁם גַּם מֵאָז דַּבֶּרְךָ אֶל עַבְדֶּךָ" ("from yesterday, and from the day before, and from ever since you have spoken to your servant"). What is the meaning of Moshe's words, and when did his speech problems begin – from birth or only at a much later point? At first glance, the first two phrases ("גַּם מִתְּמוֹל גַּם מִשִּׁלְשֹׁם") appear to be moving backwards in time. This, however, creates a difficulty with the third phrase ("גַּם מֵאָז דַּבֶּרְךָ אֶל עַבְדֶּךָ"), as was not the Burning Bush the first time that Hashem spoke to Moshe?3
Additionally, Moshe's reluctance to be a public speaker manifests itself only until the Exodus. In Egypt, in his interactions with both the Israelites and Paroh, he is generally accompanied by Aharon who serves as his spokesman. However, after the Exodus, Moshe appears more than capable of speaking for himself,4 and in Sefer Devarim Moshe delivers eloquent addresses without the assistance of Aharon (who is already deceased).5 Was Moshe's disability cured, did it affect him only in certain situations, or is it just that the Torah does not continue to tell us about the spokespersons who assisted him?
The different understandings of Moshe's condition also raise the questions of its cause and why Hashem would choose to send a blemished messenger. Was it merely happenchance or was there some deeper message that Hashem was attempting to convey?