The Gemorah in Shabbos says that anyone who says “vayechulu” becomes a partner in the creation of the world. By saying these verses, we are giving testimony that Hashem created the world. As with all testimony, this should be said while standing, and also with at least two men.
There is a disaagreement between the Mishna Berurah and the Chazon Ish whether one should seek this testimony. If you did not finish davening until after everyone finished “vayechulu”, the opinion of the Mishneh Berura 268:19 is to join with someone else to say together “vayechulu”. The Chazon Ish argues. He says that if the tzibbur already finished, you should not look for someone else to say it with you. The custom of most people is like the Mishna Berurah.

Rabbi Tzvi Aryeh Hyman, Mir Yeshiva
If you have any questions or comments please send them to:
[email protected]