But if you hearken attentively to his voice is literally “But if hearing you [singular] hear to his voice.” This repetition of the verb is the emphatic form, so attentively or something similar must be added. New International Version has “If you listen carefully to what he says,” but the stronger meaning of “obey” (Good News Translation) is also suggested, as in verse 21. Childs has “But if you will really obey him,” and Contemporary English Version has “If you faithfully obey him.”

And do all that I say suddenly shifts from third person (his voice) to first person (I say). This should not be a problem in translation, if it is clear that the angel represents Yahweh himself and speaks for him. Otherwise it will be better to say “do all that he says.”

Then I will be an enemy to your enemies basically means “I will be hostile to those who are hostile to you [singular],” or “I will hate those who hate you.” (The same word for enemy is used in verse 4.) And an adversary to your adversaries says the same thing, using a different word that also means “to be hostile to” or “to be in conflict with.” Good News Translation combines the two into one: “I will fight against all your enemies.” Contemporary English Version has “I will be a fierce enemy of your enemies.” In certain languages where “enemies” will be rendered as “those who hate you,” one may say “I will fight fiercely against all those people who hate you.”

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 .