וַיֹּ֤אמֶר אֲלֵיהֶם֙ מֹשֶׁ֔ה אִֽם־תַּעֲשׂ֖וּן אֶת־הַדָּבָ֣ר הַזֶּ֑ה אִם־תֵּחָֽלְצ֛וּ לִפְנֵ֥י יְהוָ֖ה לַמִּלְחָמָֽה׃
Entonces les respondió Moisés: Si lo hiciereis así, si os apercibiereis para ir delante de SEÑOR á la guerra,
Da'at Zekenim
יחי ראובן ואל ימות, “may Reuven live and not die.” When the tribe of Reuven will fulfill its promise and march as vanguard in front of the army conquering the land of Canaan, (together with the tribe of Gad and half the tribe of Menashe, as per Numbers 32,20-42) they will not suffer a single casualty during that campaign.