en_tn/num/06/21.md

he must keep the obligations of the vow he has taken, to keep the promise indicated by the law for the Nazirite

These two phrases mean basically the same thing and are combined for emphasis. (See: rc://en/ta/man/translate/figs-parallelism)

the promise indicated by the law for the Nazirite

AT: "the promise that the law for the Nazirite indicates" (See: rc://en/ta/man/translate/figs-activepassive)