Thus says the LORD is the special messenger formula used repeatedly in the negotiations with the Pharaoh. This formula here introduces another embedded quote at the third level. The main quotation begins in verse 14 (first level), with an embedded quote introduced in verse 16 (second level), and here a quote embedded into that quote (third level). By this refers to the plague that will soon take place, and so it introduces the warning to the Pharaoh. You shall know means “you will find out” (Good News Translation), or “you shall learn” (Jerusalem Bible). It refers back to the question raised by the king in 5.2. I am the LORD is the self-introductory formula discussed at 6.2. Other translation models for this sentence are ‘Yahweh says, “I am going to do something to show that I am really Yahweh,” ’ or “Yahweh says that he is going to do something that will show [or, prove to] you that he is really Yahweh.”
Behold is not omitted here by Good News Translation, as in verse 16, for it is a command for the king to “Look” (Good News Translation). Probably Moses is holding up his rod as he speaks. I will strike the water presents a problem, for the Hebrew does not clarify whether this is still the third level quote, where the LORD is speaking, or the second level quote, where Moses is speaking. As the quotation marks in Revised Standard Version present it, the I refers to the LORD, meaning that the LORD will be the one to strike the water. (This is also suggested in verse 25.) But this is unlikely, since the statement goes on to refer to the rod that is in my hand, meaning Moses’ hand (although verse 19a seems to put the rod in Aaron’s hand). For this reason New English Bible closes the third level quote before the word behold so that the I will refer to Moses (“… the LORD says, ‘By this you shall know that I am the LORD.’ With this rod that I have in my hand…”). Good News Translation avoids the third level quote entirely, but clearly puts the words in Moses’ mouth: “Look, I am going to strike….” This is probably the intended meaning of the text as we have it. Other translations prefer to preserve the ambiguity.
The rod that is in my hand may be shortened to “the staff I hold” (New American Bible) or simply “this stick” (Good News Translation). (See verse 15.) And it shall be turned to blood refers to the water in the river, which will be “changed into,” “become,” or “will turn into” blood. This indicates a change in substance, not just a change in color. The Hebrew term refers to the blood of either man or animal.
Quoted with permission from Osborn, Noel D. and Hatton, Howard A. A Handbook on Exodus. (UBS Helps for Translators). New York: UBS, 1999. For this and other handbooks for translators see here .