And the LORD did so refers to what the LORD actually did two days after Moses received his instructions (verses 20-23). We must assume that Moses actually confronted the king the following day (verse 20), but this is only implied. In some languages and cultures it may be necessary to make it explicit. One may expand this phrase and say “The LORD did exactly what Moses told the king he would do.” Or one may have to add, either here or at the end of verse 23, these words: “Moses warned the king that the LORD would send a plague of flies.”

There came great swarms of flies now describes exactly what happened. The word translated “great” literally means “heavy.” So various translations have “dense” (New English Bible, New International Version), “thick” (New American Bible), “heavy” (New Jewish Publication Society’s Tanakh), “vast” (Translator’s Old Testament), or even “grievous swarms of flies” (American Standard Version). The verb came may be made more descriptive with words such as “invaded” (New Jewish Publication Society’s Tanakh), “infested” (New English Bible), or “poured into” (New International Version).

In the Hebrew text swarms is the subject of the verb came, but Good News Translation has “The LORD sent great swarms of flies.” A footnote in Good News Translation would have been helpful to show that this is based on a few ancient versions, which have “he brought swarms.” But Good News Translation also omits the opening words, And the LORD did so, which are not needed with this different reading. If the translation follows the example of Good News Translation, however, a footnote should be added. Another solution is to add the words “as he said he would” and translate “The LORD sent great swarms of flies as he said he would” or “… as he had promised.”

Into the house of Pharaoh means “into the king’s palace” (Good News Translation). Into his servants’ houses means “into the mansions of the members of his court” (Durham). In all the land of Egypt may be shortened to “in all of Egypt” (New Revised Standard Version), since it is used again in the clause the land was ruined by reason of the flies. The verb ruined is imperfect in form, so it may be understood in the sense of incomplete action. New English Bible has “the land was threatened with ruin,” and Translator’s Old Testament has “the land was being ruined.” But most translations take it as completed action, “The whole land of Egypt was brought to ruin by the flies” (Good News Translation). In languages that do not have the passive voice, one may say, for example, “And the flies devastated [or, ruined] the whole land of Egypt.”

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 .