Exodus 4:6-9: A Leprous Hand, and Waters of Blood
Verse 6: And the LORD said furthermore unto him, Put now thine hand into thy bosom. And he put his hand into his bosom: and when he took it out, behold, his hand was leprous (Num. 12:10; 2 Kings 5:27) as snow.
[Leprous after the likeness of snow] That is, Because of the leprosy it was white, just like snow (Vatablus). For there is a certain type of white leprosy (Munster). That leprosy is the worst which defiles the skin with white spots: see Numbers 12:10 (Junius).
As snow: For whiteness. See Numbers 12:10. Hereby God would suggest to them how soon he could weaken and destroy the hard and strong hand by which the Egyptians tyrannised over them. It might also be done to keep Moses humble and depending upon God, and to teach him and Israel to ascribe all the future miracles not to the hand of Moses, which was weak and liable to many distempers, but wholly to the Divine power and goodness.
Verse 7: And he said, Put thine hand into thy bosom again. And he put his hand into his bosom again; and plucked it out of his bosom, and, behold, (Deut. 32:39; Num. 12:13, 14; 2 Kings 5:14; Matt. 8:3) it was turned again as his other flesh.
[And it was like unto the rest of his flesh (similarly Junius and Tremellius, Arabic), שָׁ֖בָה כִּבְשָׂרֽוֹ׃] It was turned back just like his flesh (thus most interpreters); it was restored unto the color of flesh (Arabic).
Verse 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.
[Neither hearken to the voice of the first sign] It is personification. For God speaks to us by miracles (Vatablus, Ainsworth); He adds His word to the signs, as in Exodus 4:30; Ezekiel 1:28; Job 4:16 (Ainsworth). That is, if they will not believe the words which thou wilt have confirmed by the prior miracle (Vatablus, Fagius). The voice of the sign, that is, the voice confirmed by the sign (Menochius).
To the voice of the first sign; to the voice or word of God delivered and confirmed by the first sign. For Moses did not make dumb shows before them, but acquainted them with the mind of God therein. Or he saith the voice, to note that God’s works have a voice to speak to us, which we must diligently observe. See Micah 6:9.
Verse 9: And it shall come to pass, if they will not believe also 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 (Ex. 7:19) the water which thou takest out of the river shall become (Heb. shall be and shall be) blood upon the dry land.
The river Nile, well known to Moses, and called so by way of eminency, as Euphrates also is.
[Whatever thou wilt have drawn out, etc., וְהָי֤וּ הַמַּ֙יִם֙—וְהָי֥וּ לְדָ֖ם] And the waters shall be, they shall be, I say, blood (Munster, Tigurinus). For it shall change so that it might become blood (Arabic). Let them be changed, let them be changed, I say, into blood (Junius and Tremellius, similarly Pagnine, Ainsworth).
Shall become; Hebrew, shall be, even shall be, that is, it shall assuredly be so.
[Into blood] A reproach arising from the infants suffocated in the waters, and a foresignification of their death in the Red Sea (Menochius).
 Hebrew: וַיֹּאמֶר֩ יְהוָ֙ה ל֜וֹ ע֗וֹד הָֽבֵא־נָ֤א יָֽדְךָ֙ בְּחֵיקֶ֔ךָ וַיָּבֵ֥א יָד֖וֹ בְּחֵיק֑וֹ וַיּ֣וֹצִאָ֔הּ וְהִנֵּ֥ה יָד֖וֹ מְצֹרַ֥עַת כַּשָּֽׁלֶג׃
 Hebrew: וַיֹּ֗אמֶר הָשֵׁ֤ב יָֽדְךָ֙ אֶל־חֵיקֶ֔ךָ וַיָּ֥שֶׁב יָד֖וֹ אֶל־חֵיק֑וֹ וַיּֽוֹצִאָהּ֙ מֵֽחֵיק֔וֹ וְהִנֵּה־שָׁ֖בָה כִּבְשָׂרֽוֹ׃
 Hebrew: וְהָיָה֙ אִם־לֹ֣א יַאֲמִ֣ינוּ לָ֔ךְ וְלֹ֣א יִשְׁמְע֔וּ לְקֹ֖ל הָאֹ֣ת הָרִאשׁ֑וֹן וְהֶֽאֱמִ֔ינוּ לְקֹ֖ל הָאֹ֥ת הָאַחֲרֽוֹן׃
 Hebrew: וְהָיָ֡ה אִם־לֹ֣א יַאֲמִ֡ינוּ גַּם֩ לִשְׁנֵ֙י הָאֹת֜וֹת הָאֵ֗לֶּה וְלֹ֤א יִשְׁמְעוּן֙ לְקֹלֶ֔ךָ וְלָקַחְתָּ֙ מִמֵּימֵ֣י הַיְאֹ֔ר וְשָׁפַכְתָּ֖ הַיַּבָּשָׁ֑ה וְהָי֤וּ הַמַּ֙יִם֙ אֲשֶׁ֣ר תִּקַּ֣ח מִן־הַיְאֹ֔ר וְהָי֥וּ לְדָ֖ם בַּיַּבָּֽשֶׁת׃
 Hebrew: וְהָיוּ—וְהָיוּ.
 Exodus 4:9b: “…and the water shall be (וְהָי֤וּ הַמַּ֙יִם֙) which thou takest out of the river, even they shall become blood (וְהָי֥וּ לְדָ֖ם) upon the dry land.”