Up, sanctify the people
The word "up" not only signifies getting up from the ground on which he lay, but to bestir himself, and to be active in what he would now be enjoined and directed to do, and in the first place to "sanctify the people", that is, by giving them orders to do it themselves:
and say, sanctify yourselves against tomorrow;
either by some ceremonial ablutions, or by the performance of moral duties, as prayer, repentance, and good works; or rather, they were to "prepare" themselves, as the Targum and Kimchi interpret it, to get ready against the morrow, and expect to be thoroughly searched, in order to find out the person who had taken the accursed thing:
for thus saith the Lord God of Israel, [there is] an accursed thing in
the midst of thee, O Israel;
an accursed person, who had taken of what was devoted to the Lord for his own use, and so accursed:
thou canst not stand before thine enemies, until ye take away the
accursed thing from among you;
by putting him to death.
The Brenton translation of the Septuagint is in the public domain.