And it shall come to pass, if they will not believe thee,.... Will not give credit to the commission he had from God, but question the truth of it: neither hearken to the voice of the first sign; which miracle wrought, spoke plain enough that he that wrought it, or for whose sake it was wrought, must be one come from God, or such a miracle would never be wrought by him or for him; but should any of the Israelites be still incredulous, it is supposed: that they will believe the voice of the latter sign; which had a voice in it commanding belief that he was a messenger of God; the first sign respects his rod, the other his hand.