Exodus 4:10

I am not eloquent. That he who had been “mighty in words and in deeds” (Acts 7:22) should claim difficulty in speaking seems unwarranted, in view of God’s promise to prosper his mission. His long absence from Egypt and the fact that he had not spoken its language during the sojourn in Midian without doubt made him feel unqualified to go before Pharaoh, but he should have been ready to trust in God. It has been suggested that Moses feared to speak in Hebrew because he had been living among the Midianites. This cannot have been the reason, however, since Midianite inscriptions differ but little from ancient Hebrew. The Jewish tradition that Moses had difficulty in pronouncing certain Hebrew letters has no substantiation either.