We must go is literally “we will go,” but Moses is demanding what must be. Three days’ journey means walking “a distance of three days” (New Jewish Publication Society’s Tanakh), one-way. Into the wilderness would have been understood by the king as moving eastward beyond the populated area of Egypt. It should be noted that these same words appear in 3.18 and 5.3 in the form of a request, but here they express a demand.

And sacrifice to the LORD means to “offer sacrifices” to Yahweh (as in verse 26). To the LORD our God, of course, will use the exclusive form of our, for Yahweh was not the Pharaoh’s God. As he will command us means “just as he is telling us” (Durham). New Revised Standard Version has “as he commands us.” The tense of the verb, however, is not clearly indicated, although the command has already been given. Good News Translation‘s “just as he commanded us” does not allow for future instruction. Translator’s Old Testament does allow for this: “and then offer to the LORD our God whatever sacrifices he may demand.” It is possible to restructure this verse, putting the final sentence first: “Yahweh our [exclusive] God has ordered us to walk three days into the wilderness to sacrifice to him whatever animals he demands. That’s what we must do.”

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 .