These are still words to be spoken by the father to the children. For when Pharaoh stubbornly refused to let us go is literally “And it was that Pharaoh made hard to let us go.” The word used for “hard” is the same as in 7.3, but the heart is not mentioned here, although in certain languages it will still be possible to use figurative expressions or idioms employing the heart (or, liver) and so on; for example, “When the king of Egypt set his heart and refused” or “The king of Egypt made his heart [liver] hard and refused.” Various attempts have been made to reflect the Hebrew. For example, Fox has “when Pharaoh hardened [his heart] against sending us free.” And Durham has “when Pharaoh was stubborn-minded about sending us forth.” Good News Translation is clear: “When the king of Egypt was stubborn and refused to let us go.” Contemporary English Version has “The king stubbornly refused to set us free.” The us should be inclusive, as in verse 14.
The LORD slew uses a different word from that in 12.23 and 27. Here it clearly means to kill, as in 2.14 (see the comment there). All the first-born in the land of Egypt means the firstborn son in every Egyptian family. Both the first-born of man is the same as verse 13, distinguishing the humans (ʾadam) from the animals. And the first-born of cattle also means “firstborn male.” The word for cattle means “animals” (New Revised Standard Version), including more than just the domesticated animals. The word is the same as in verse 12.
Therefore means “That is why” (Good News Translation), and I sacrifice to the LORD may be understood as “we sacrifice” (inclusive). The participle is used for sacrifice, suggesting continuous action. So Durham has “For that reason, I am sacrificing to Yahweh.” (“Sacrifice” is discussed at 3.18b.) All the males that first open the womb is literally “all firstborn of the womb, males.” New American Bible has “everything of the male sex that opens the womb.” This refers, of course, only to the animals, as the next clause makes clear. But in many languages it will be helpful to make this explicit and say, for example, “every firstborn male of every animal.”
But all the first-born of my sons should be understood as singular if spoken by one father, as in Translator’s Old Testament (“my first-born son”), for each father would have only one firstborn son. New Revised Standard Version‘s “every firstborn of my sons” is equally confusing because the Hebrew includes the word for all (or, “every”). But this should be understood as an instruction to all fathers; it does not mean that the grandfather was responsible for the firstborn of each of his sons. No Israelite father was exempt from this requirement to redeem his own firstborn son. Good News Translation avoids this misunderstanding by changing the I to “we,” and the my to “our”: “our first-born sons.” I redeem, as explained in verse 13, means to “buy back.”
An alternative translation model for this verse is:
• The king of Egypt made his heart hard and refused to free us [inclusive]. So the LORD [or, Yahweh] killed the firstborn male of every animal, and the firstborn son of every Egyptian family. That is why we [inclusive] slaughter every firstborn male of every animal and offer it to the LORD, and we buy back our 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 .