And Moses said unto the LORD, O my Lord, I am not eloquent, neither heretofore, nor since thou hast spoken unto thy servant: but I am slow of speech, and of a slow tongue. I am not eloquent - לא איש דברים lo ish debarim, I am not a man of words; a periphrasis common in the Scriptures. So Job 11:2, איש שפתים ish sephathayim, a man of lips, signifies one that is talkative. Psalms 140:11, איש לשון ish lashon, a man of tongue, signifies a prattler. But how could it be said that Moses was not eloquent, when St. Stephen asserts, Acts 7:22, that he was mighty in words as well as in deeds? There are three ways of solving this difficulty:
1. Moses might have had some natural infirmity, of a late standing, which at that time rendered it impossible for him to speak readily, and which he afterwards overcame; so that though he was not then a man of words, yet he might afterwards have been mighty in words as well as deeds.
2. It is possible he was not intimately acquainted with the Hebrew tongue, so as to speak clearly and distinctly in it. The first forty years of his life he had spent in Egypt, chiefly at court; and though it is very probable there was an affinity between the two languages, yet they certainly were not the same. The last forty he had spent in Midian, and it is not likely that the pure Hebrew tongue prevailed there, though it is probable that a dialect of it was there spoken. On these accounts Moses might find it difficult to express himself with that readiness and persuasive flow of language, which he might deem essentially necessary on such a momentous occasion; as he would frequently be obliged to consult his memory for proper expressions, which would necessarily produce frequent hesitation, and general slowness of utterance, which he might think would ill suit an ambassador of God.
3. Though Moses was slow of speech, yet when acting as the messenger of God his word was with power, for at his command the plagues came and the plagues were stayed; thus was he mighty in words as well as in deeds: and this is probably the meaning of St. Stephen.
By the expression, neither heretofore, nor since thou hast spoken unto thy servant, he might possibly mean that the natural inaptitude to speak readily, which he had felt, he continued to feel, even since God had begun to discover himself; for though he had wrought several miracles for him, yet he had not healed this infirmity. See Clarke on Exodus 6:12 (note).