Q. Why is a chapter from the Mishnah included in the Friday evening service?
A. The second chapter of the Mishnah Shabbat, BaMeh Madlikin, deals with the Shabbat lights. Some say it is read before the actual onset of Shabbat to remind anyone who has not yet kindled the lights to go and do so.
Another view sees it as an implicit attack on the Karaites who said that not kindling a fire on the Sabbath day meant not having a fire burning. Rabbinic Judaism believes that if a fire is lit or lights are kindled before Shabbat we may enjoy them during Shabbat.