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. 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.
The verse belongs to the sending of Moses to deliver Israel when the time for deliverance had come. The commission was given at Horeb, the mountain of God. There God appeared in a bush that burned without being consumed. There He spoke as the God of Abraham, Isaac, and Jacob, the Angel of the covenant, and required humble reverence such as removing shoes on holy ground.
While in the land of Midian, Moses pleaded for a sign to confirm that his message was truly from heaven. God answered by accrediting a humble shepherd carrying only a rod, making that rod the symbol of His power, and by working in that lowly way He would pour contempt on human pride. The assuring signs were the rod becoming a serpent and the hand turning leprous. By such signs and wonderful works God would make Pharaoh and the Egyptians fear so they would not dare to harm Moses, and would convince the king and his people that One greater than Moses was manifesting power before them.
Yet even after many miracles performed before Pharaoh in the sight of the people, they would still not let Israel go. Moses' pleading for assurance parallels the later pleading of Gideon in the presence of the heavenly messenger, of Elisha just before the ascension of his master, and of Hezekiah when he asked for a sign that the Lord would heal him.