They will hearken to your voice means that they “will listen to what you say to them” (Good News Translation), or simply, they “will listen to you” (New International Version, Contemporary English Version). But this is not passive listening; the implication is that they will believe what Moses tells them and be ready to follow his instructions. So one may translate “They will believe and obey you.” The they may be understood as “My people,” meaning all the Israelites, but the nearest antecedent in verse 16 is “The elders of Israel” (New International Version), mentioned also in the following clause, and this is likely what is meant.
You and the elders of Israel shall go is literally “you [singular] shall go, you [singular] and the elders of Israel.” Good News Translation‘s “you must go with the leaders of Israel” may be misunderstood, suggesting that Moses would only accompany the elders rather than lead them. A better model is “You must take the leaders of Israel and go” (similarly New Jewish Publication Society’s Tanakh). Many languages will naturally say “You [plural] and the leaders of Israel shall go.” But if it is necessary to be more specific, then Moses should be the one whom the elders accompany. And say to him is literally “and you [plural] shall say to him.”
The LORD, the God of the Hebrews identifies the Hebrews’ God by his personal name, YHWH. So one may translate as “Yahweh, the God of the Hebrews.” (Compare 3.2a and 15.) The Hebrews refers to the larger group of Semitic people of which the Israelites were a part. The origin of the word ʿbri (“Hebrew”) is not certain. Most of the time it is used in reference to the Israelites, but it may originally have referred to the descendants of Eber, an ancestor of Abraham and several Semitic groups (Gen 10.24-25). The translator should never substitute “Israelites” for Hebrews unless the context clearly refers only to the descendants of Jacob and excludes any other descendants of Abraham. Has met with us is literally “he has happened himself on us.” In its present context this can mean “has revealed himself to us,” “has come to meet us” (Jerusalem Bible), or “has encountered us” (New Jerusalem Bible). It conveys the idea of an unexpected meeting initiated by the LORD himself. With us may suggest that God was planning to reveal himself to the elders as well as to Moses, but it is better to understand it here in the sense that Moses was to be the representative of the people. In languages that distinguish between inclusive and exclusive pronouns, the pronoun us is exclusive, since it excludes the king.
And now, we pray you, is a polite way of introducing a request to a king, but the expression we pray you is somewhat archaic in English. The Hebrew particle that shows politeness may be more naturally translated as “please,” as in New Jerusalem Bible: “So now please allow us….” Good News Translation and other English translations try to reflect this politeness by using more formal language. Let us go is therefore not a demand but a request, as “allow us to travel” (Good News Translation) implies. One may also say “please allow us to travel.” In languages that must state the mode of travel, one may express this as “please allow us to walk…,” as the majority of the Israelites would presumably have traveled by foot.
A three days’ journey into the wilderness should be interpreted as “a distance of three days” (New Jewish Publication Society’s Tanakh) or “the distance one walks in three days” rather than a round trip within three days. Good News Translation‘s “allow us to travel three days into the desert” is a bit ambiguous. This request implies a return to Egypt after a week or so, even though they would secretly plan to continue on to the promised land. The problem of wilderness versus “desert” is discussed at 3.1.
That we may sacrifice to the LORD our God is a sincere request that would not have surprised the king. While Israel’s form of sacrifice may have been different from that practiced in Egypt (see 8.26), the word implies a ritual killing of animals without specifying what kind. If the translation must specify, then large animals like cattle should be understood; for example, “slaughter cattle to offer to Yahweh, our [exclusive] God.” The idea was “to offer sacrifices to the LORD,” identifying their God by name.
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 .