For the LORD will pass through uses the same verb as verse 12 but without repeating “the land of Egypt.” Good News Translation adds “Egypt” to make it clear. The word for, the usual conjunction waw, can also introduce a temporal clause, “When the LORD goes through Egypt” (Good News Translation). (Similar are New Jewish Publication Society’s Tanakh, New International Version, and New Jerusalem Bible.) Contemporary English Version‘s model helps to place the event on a particular night, “During that night, the LORD will go through the country of Egypt.” To slay the Egyptians is the purpose for Yahweh’s passing through, but slay means to injure with a blow or to strike with a plague (as in 8.2). In this context, however, “to kill” (Good News Translation) is implied. The word is used again at the end of this verse. It will be helpful to indicate that the LORD will not slay every Egyptian. One can do this by repeating the words “firstborn son”; for example, “and kill the firstborn son in every Egyptian family” (so also Contemporary English Version).

And when he sees the blood really means “whenever” (Moffatt), implying that Yahweh will examine every house in Egypt. On the lintel and on the two doorposts is discussed at verse 7. The LORD will pass over the door uses the verb pasach (see the comment at verse 27). The word for door means the entrance to the house, so in languages where the idea of “pass over” will not work, one may say “Yahweh will pass by that doorway” or “… pass by that house,” that is, without entering. One may also say “will not come into your house.” Good News Translation unfortunately omits this idea here.

And will not allow the destroyer uses the same word for “destroy” as verse 13. Here, however, it is used as a noun, with the definite article, referring possibly to an “Angel of Death” (Good News Translation) or to some impersonal destructive force. If translators use the idea of “Angel of Death,” another way to express this is “his [Yahweh’s] angel [or, helper] who causes death.” The context suggests that the destroyer would accompany Yahweh and be ready to enter the houses whenever instructed to do so. Your houses refers to the houses of the Israelites. To slay you is simply “to slay,” with you implied. This is the same word used earlier in this verse. Again, it is possible to say “and not kill your firstborn sons.”

An alternative translation model for this verse is:

• During that night the LORD will go through the land of Egypt and kill the firstborn son in every Egyptian family. He will see the blood on the top and sides of your doors and will not allow his angel [or, helper] who causes death to enter your houses and kill your firstborn sons.

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 .