Else introduces a conditional clause that here serves as a warning. This is further emphasized by the word behold at the end of the clause. Good News Translation combines behold with else and begins “I warn you that if….” If you will not let my people go repeats the same words as in verse 20 with the negative. The context is clear enough that this may seem unnecessary or unnatural in translation in many languages. However, if it is natural style in a receptor language, translators should keep it. Good News Translation condenses to “if you refuse,” and Contemporary English Version has “If you don’t.”

I will send swarms of flies on you is the official announcement of the fourth plague, but this is still a part of Yahweh’s words to Moses. The I, of course, is Yahweh, the LORD, and the you is singular, referring to the Pharaoh. Again there may be an intentional play on the word send, which is the same word used in let my people go. (See verse 20 and the discussion at 7.16.)

Swarms of flies translates just one word in the Hebrew, which seems to be a generic term for “insects.” The word is a collective noun that comes from the verb “to mix,” so the idea of swarms is suggested. Most translations identify the insects as flies because of the early interpretation of “dog-flies” in the ancient Greek translation, the Septuagint. So Jerusalem Bible has “gadflies” and New Jerusalem Bible has “horseflies.” (Durham translates this term as “a mixed swarm of flying insects.”) They were probably large flies that could leave a painful bite on animals as well as on humans. Flies should present no problem for translators, as such large biting insects are common almost everywhere in the world. However, in cases where biting flies are unknown, one may translate, for example, “a swarm of flying insects that bite.”

On you is singular, meaning on the king himself. And your servants means “your officials” (New Revised Standard Version, Good News Translation, Contemporary English Version), or “your courtiers” (New English Bible, New Jewish Publication Society’s Tanakh), or “the members of your court” (Durham). Your people means the king’s subjects, the Egyptians themselves. And into your houses would refer to all the buildings in the palace complex, for the your is still singular.

And the houses of the Egyptians begins a new clause, this time including all the Egyptian houses throughout the country. Shall be filled with swarms of flies is certainly a slight exaggeration, but the idea is clear; there would be no place where the Egyptians could escape from these terrible insects. An alternative translation model is to combine the phrase and into your houses and the clause and the houses of the Egyptians shall be filled, and translate “Houses all over Egypt will be full….”

And also the ground probably includes all of the out-of-doors, although the following phrase is ambiguous. On which they stand is literally “where they [are] upon it.” The word they may refer either to where their houses are built or to wherever the people may go. The ambiguity is certainly not intentional, so we should follow either Good News Translation, “and the ground will be covered with them,” or New Revised Standard Version, “so also the land where they live,” or one may say “they will cover the ground everywhere.”

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 .