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.

And the heavens and the earth were completed and [so were] all their hosts. And God completed by the seventh day His work which He had done, and He abstained on the seventh day, from all His work which He had done. And God blessed the seventh day and sanctified it for on it He abstained from all His work which God had created to do.