Êxodo 4:1

¹ Então respondeu Moisés: Mas eis que não me crerão, nem ouvirão a minha voz, pois dirão: O Senhor não te apareceu.

Dumb

To be dumb, or unable to speak, as in Exodus 4:11 and Isaiah 35:6, signifies people who cannot confess the Lord because they are ignorant of the truth. (Arcana Coelestia 6988, Apocalypse Explained 455)

In Mark 9:25, this signifies one who does not want to perceive and understand truth. (Apocalypse Explained 556)

⁶ Then the lame man will leap like a deer, and the tongue of the mute will sing; for waters will break out in the wilderness, and streams in the desert.