Do not go up is the opposite command in 13.17 (see the comments there).

Lest you be struck down before your enemies, for the LORD is not among you is literally “for the LORD is not in your midst, so that you are not struck down before your enemies,” which gives the reason why the Israelites should not invade Canaan. Good News Translation follows the original clause order here by saying “The LORD is not with you, and your enemies will defeat you.” The Hebrew verb rendered be struck down refers figuratively to defeat. For languages that do not use passive verbs, they may follow Good News Translation here. In this context the LORD is not among you means the LORD will not come with the people to protect them (see verse 14). This idea is connected with the notion that the Covenant Box was the token of the LORD’s personal presence in the midst of his people. (Verse 44 refers to this idea more explicitly.) A good model for this clause is “the LORD is not coming along with you.” Revised English Bible says “you will not have the LORD 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 .