וְעָמְד֧וּ שְׁנֵֽי־הָאֲנָשִׁ֛ים אֲשֶׁר־לָהֶ֥ם הָרִ֖יב לִפְנֵ֣י יְהוָ֑ה לִפְנֵ֤י הַכֹּֽהֲנִים֙ וְהַשֹּׁ֣פְטִ֔ים אֲשֶׁ֥ר יִהְי֖וּ בַּיָּמִ֥ים הָהֵֽם׃
then both the men, between whom the controversy is, shall stand before the LORD, before the priests and the judges that shall be in those days.
Siddur Sefard
After the Shemoneh Esrei has been said, the entire congregation repeats וַיְכֻלּוּ , in testimony of our belief that God created heaven and earth. According to Halacha, when one is a witness, he must stand and declare his testimony aloud.