Exodus 4:10
8 “If they do not believe you or pay attention to the former sign, then they may believe the latter sign. 9 And if they do not believe even these two signs or listen to you, then take some water from the Nile and pour it out on the dry ground. The water you take out of the Nile will become blood on the dry ground.” 10 Then Moses said to the Lord, “O my Lord, I am not an eloquent man, neither in the past nor since you have spoken to your servant, for I am slow of speech and slow of tongue.” 11 The Lord said to him, “Who gave a mouth to man, or who makes a person mute or deaf or seeing or blind? Is it not I, the Lord? 12 So now go, and I will be with your mouth and will teach you what you must say.”
Ezekiel 3:5
3 He said to me, “Son of man, feed your stomach and fill your belly with this scroll I am giving to you.” So I ate it, and it was sweet like honey in my mouth. 4 He said to me, “Son of man, go to the house of Israel and speak my words to them. 5 For you are not being sent to a people of unintelligible speech and difficult language, but to the house of Israel— 6 not to many peoples of unintelligible speech and difficult language, whose words you cannot understand. Surely if I had sent you to them, they would listen to you! 7 But the house of Israel is unwilling to listen to you, because they are not willing to listen to me, for the whole house of Israel is hardheaded and hardhearted.
Notes and References
"... A common misconception of the Moses character is that the Exodus narrative portrays him as having had a speech impediment. At the bush that did not burn up, Moses entered into a conversation with yhwh that ended with him being sent to Egypt to lead God’s people out of bondage. Moses pushed back on this assignment with obvious reluctance in one final argument, which is recorded in Exodus 4:10–13. He began this last phase of reticence by saying, “O my Lord, I am not eloquent, neither before nor since You have spoken to Your servant; but I am slow of speech and slow of tongue”. However, Ezekiel 3:5–6 uses the same phrase “slow of tongue” that Moses does to refer to foreign languages that are unintelligible (compare Isaiah 33:19). “Heavy” usually refers to a medical condition, but here the use is extended to refer to linguistic difficulties. Carol Myers makes the connection to an Egyptian ritual of “opening the mouth,” and surmises that there was no medical condition in mind in Exodus 4. In addition, this “slowness” was not associated with a stuttering problem when this story was recounted by Stephen, one of the Christian church’s first deacons, in Acts 7:22. Stephen is recorded as saying that Moses, during his life growing up as an Egyptian prince, “was learned in all the wisdom of the Egyptians, and was mighty in words and deeds”. Being “mighty in words” obviously cannot reflect a speech impediment. Thus, those who held to the authenticity of the story by that late date seemed to understand Moses’s slowness of speech to be something different than a problem with speaking ..."
Wells, A. Rahel and L. S. Baker Jr. "Egyptian Language Practice: A Model for Hebrew Poetic Use?" in Baker, Leslie Scott, et al (eds.) xploring the Composition of the Pentateuch (pp. 49-65) Eisenbrauns, 2020