Verse 13 gives the historical background of verse 12 and recalls the Exodus (see Exo 11.5; 13.2, 15). Good News Translation has reversed the order of these verses and combined them in order to present a sequence that is easier to follow in English.
Behold, I have taken the Levites from among the people of Israel instead of every first-born that opens the womb among the people of Israel: Behold renders the Hebrew word hinneh, which emphasizes what the LORD is saying here. He declares that he himself has chosen the male Levites to belong to him in a special way in place of the firstborn sons of Israel. The Hebrew expression rendered Behold, I have taken (literally “And I, behold, I take”) should not be translated in the past tense. A past tense rendering does not take the function of the Hebrew verb into account here. A more accurate translation that fits the context better is “I hereby take” (New Jewish Publication Society’s Tanakh). Every first-born refers to every firstborn son in this context. That opens the womb renders a technical Hebrew expression that has the same meaning as first-born. A literal rendering of this phrase as in Revised Standard Version may be offensive or embarrassing in the target language. If a local idiom is not available, then this phrase may have to be left implied.
The Levites shall be mine, for all the first-born are mine: All the firstborn sons of the Israelites belonged to God, but he accepted the male Levites as a substitute for them. For renders the Hebrew connector ki, which introduces and emphasizes why the Levites belonged to God. Bible en français courant and Parole de Vie translate it correctly as an emphatic particle here, saying “Indeed.”
On the day that I slew all the first-born in the land of Egypt: I slew is literally “I struck/attacked.” In this context it means “I killed” (Good News Translation). Here it is important to avoid the negative overtones of a verb like “murdered” in English. The first-born in the land of Egypt refers to the firstborn sons of the Egyptians.
I consecrated for my own all the first-born in Israel, both of man and of beast: I consecrated for my own is literally “I declared holy to myself,” which may be rendered “I claimed for myself” (New Afrikaans Version) or “I set apart [or, chose] for myself” (New Living Translation). All the first-born in Israel, both of man and of beast refers to all the firstborn sons and firstborn male animals of the Israelites. Man renders a generic Hebrew word for human beings, and beast translates a generic word for domestic animals. Contemporary English Version renders this whole phrase as “the first-born sons in every Israelite family and the first-born males of their flocks and herds.”
They shall be mine: In the immediate context the pronoun they refers to all the first-born in Israel, both of man and of beast. La Nouvelle Bible Segond makes this clear by rendering this clause and the previous one as “I consecrated for my own all the firstborn in Israel; those of man as well as those of beast belong to me.” Good News Translation wrongly suggests that the pronoun they refers to the Levites.
In the last half of verse 13 the change from past tense (I consecrated) to future or present tense (shall be mine; “belong to me” in New Afrikaans Version) may be awkward in translation. If so, New Jewish Publication Society’s Tanakh provides the following helpful model: “I consecrated every first-born in Israel, man and beast, to Myself, to be Mine.”
I am the LORD: This clause gives the reason why the firstborn people and animals belong to the LORD. Bijbel in Gewone Taal makes this clear by saying “because I am the Lord.” In addition to its function as a emphatic conclusion, this formulaic divine self-designation may also be an abbreviated way of referring to certain parallel passages in the Pentateuch, for example, Lev 11.44-45. It should be translated consistently, if possible, in some distinctive manner that highlights its function; for example, Chewa has “I it is me Chauta [the LORD].”
Quoted with permission from de Regt, Lénart J. and Wendland, Ernst R. A Handbook on Numbers. (UBS Helps for Translators). Miami: UBS, 2016. For this and other handbooks for translators see here .