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)