66 The verb נֵלֵךְ (nelekh) is a Qal imperfect of the verb הָלַךְ (halakh). Here it should be given the modal nuance of obligation: “we must go.”
67 This clause is placed first in the sentence to stress the distance required. דֶּרֶךְ (derekh) is an adverbial accusative specifying how far they must go. It is in construct, so “three days” modifies it. It is a “journey of three days,” or, “a three day journey.”
68 The form is the perfect tense with a vav (ו) consecutive; it follows in the sequence: we must go … and then [must] sacrifice.”
69 The form is the imperfect tense. It could be future: “as he will tell us,” but it also could be the progressive imperfect if this is now what God is telling them to do: “as he is telling us.”

In other versions

We must go three days’ journey into the wilderness and sacrifice to the Lord our God as he tells us.”

We must take a three-day journey into the wilderness to offer sacrifices to the Lord our God, as he commands us.”

We must go a distance of three days into the wilderness and sacrifice to the Lord our God as he instructs us.”

We must take a three-day trip into the wilderness to offer sacrifices to the Lord our God, just as he has commanded us.”

We will go a journey of three days into the desert, and we will sacrifice to Yahweh our God according to what he says to us.”

We will go three days’ journey into the wilderness, and sacrifice to the Lord our God, as he shall command us.

Public Domain