Charles Ellicott Commentary Exodus 4:8

"And it shall come to pass, if they will not believe thee, neither hearken to the voice of the first sign, that they will believe the voice of the latter sign." — Exodus 4:8 (ASV)

The voice of the first sign. —Not “the voice of Moses attested by the first sign” (Rosenmüller), but the voice, which the sign itself might be regarded as speaking. (Compare Psalms 105:27, where Moses and Aaron are said to have proclaimed “the words of God’s signs.”) A miracle speaks to people.

They will believe, that is, most of them. Accustomed to the tricks of the serpent charmers (see Exodus 7:11 and commentary on that passage), the Israelites might be unmoved by the sight of the first miracle. They were then to be shown the second, which would be much more astonishing to them, having no parallel in their experience. This would persuade the majority. As some, however, might still doubt, a third sign was provided. God is patient with all reasonable doubt.