הלכה על שבת 4:2

The Sages instituted that the ḥazan recites Magen Avot or the Berakha Me’ein Sheva (a summary of the seven berakhot of the Friday night Amida) after Ma’ariv, to serve as a sort of Ḥazarat Ha-shatz (see Peninei Halakha: Shabbat 4:2 for further study).