This verse reiterates in more specific terms what has been said more generally in the previous verse.

For there the Amalekites and the Canaanites are before you means these people will attack the Israelites. The Hebrew particle ki rendered For is probably an emphatic marker here, so it is better translated “Surely.” For the Amalekites and the Canaanites, see 13.29. A model for this clause is “Indeed, the Amalekites and the Canaanites will meet you on the field of battle there” (similarly New International Readers Version).

And you shall fall by the sword is a figurative expression that means the Israelites “will die in battle” (Good News Translation; see verse 3).

Because you have turned back from following the LORD: This clause uses the imagery of physical turning away from to express the idea of refusal to obey. Contemporary English Version keeps the imagery by saying “you turned your backs on him.”

The LORD will not be with you renders a different Hebrew expression than the one translated “the LORD is not among you” in the previous verse (see the comments there), but these two clauses have the same meaning in this context. Revised Standard Version treats the previous clause as the reason for this one. Good News Translation reverses the order of these two clauses, but the relation between them remains the same as in Revised Standard Version. However, the Hebrew word rendered because normally connects the following clause with the preceding clause, not with the clause that follows. Revised English Bible shows the correct clause connections in this verse as follows:

• For in front of you are the Amalekites and Canaanites, and you will fall by the sword, because you have ceased to follow the LORD, and he will no longer be with you.

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 .