"I Saw the Sign"

(1) And Moses answered and said: ‘But, behold, they will not believe me, nor hearken unto my voice; for they will say: The lord hath not appeared unto thee.’ (2) And the LORD said unto him: ‘What is that in thy hand?’ And he said: ‘A rod.’ (3) And He said: ‘Cast it on the ground.’ And he cast it on the ground, and it became a serpent; and Moses fled from before it. (4) And the LORD said unto Moses: ‘Put forth thy hand, and take it by the tail—and he put forth his hand, and laid hold of it, and it became a rod in his hand— (5) that they may believe that the LORD, the God of their fathers, the God of Abraham, the God of Isaac, and the God of Jacob, hath appeared unto thee.’ (6) And the LORD said furthermore unto him: ‘Put now thy hand into thy bosom.’ And he put his hand into his bosom; and when he took it out, behold, his hand was leprous, as white as snow. (7) And He said: ‘Put thy hand back into thy bosom.—And he put his hand back into his bosom; and when he took it out of his bosom, behold, it was turned again as his other flesh.— (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. (9) And it shall come to pass, if they will not believe even these two signs, neither hearken unto thy voice, that thou shalt take of the water of the river, and pour it upon the dry land; and the water which thou takest out of the river shall become blood upon the dry land.’

At that time Moshe spoke inappropriately. For the Holy One, Blessed is He, had said to him "They will heed your voice," yet now [Moshe] said, "Behold they will not believe me." Immediately, the Holy One, Blessed is He, responded to him thereafter in accordance with his own opinion that the Israelites would not believe him, and gave him signs to preform in accordance with his words, although God knew those to be unfounded.

This above is a quote from Ve'Eilleh Shemos Rabbah.

Rabbi Avraham (Ibn Ezra) says, according to the plain way of Scriptural interpretation, that God had said only that the elders would believe in him, but He did not mention that the ordinary people would believe in him. Alternatively, God said only that "they will heed your voice," i.e. they would not reject him, but perhaps they would not believe in him in their hearts.

But this is not a sound interpretation.

However, it is possible that we should say that God's statement to Moses, "they will heed your voice," was not an assurance but rather the statement of an imperative. That is, "They should heed your voice," meaning that it was to be expected of them that they heed it, and that you and the elders of Israel will then come to the king of Egypt. Similarly we find elsewhere, Then Egypt- from whose midst You brought up this nation with Your power- will hear...and they will say about the inhabitants of this Land...which means "it is to be expected that it should be so." Similarly we find, Through this you shall know that I am Hashem, which is a statement of something that could be expected to occur, not something that necessarily was going to occur. The same applies to they will believe the voice of the latter sign in this chapter. And there are many other examples like this.

The most sound interpretation in my eyes is that God meant, they will heed your voice to go with you to the king and to say to him, "The God of the Hebrews happened upon us"- the statement that immediately follows they will heed your voice, for what would they lose by doing so? Now, God had informed [Moses] that "the king of Egypt would not allow them to go" and therefore Moses said, Behold they will not believe me after they see that Pharaoh does not allow them to go, and they will not heed my voice again at all, for this failed attempt to persuade Pharaoh would diminish whatever credibility I had, for they will either say Hashem did not appear to you, for if you were really God'd messenger, Pharaoh would not have defied His word, or they will say "God through the Great Ineffable Name, which signifies the Attribute of Mercy, did not appear to you, with the intention to perform supernatural signs and wonders for us, as you claim. For you are not, after all, greater than the Patriarchs, to whom God did not reveal Himself in this way, and therefore Pharaoh did not listen to you. For if it were true as you say, that you were sent through the Great Name, which signifies the Attribute of Mercy, we would have gone out of Egypt in any event, for our sins would not cause a separation between us and God's mercy.