The light emanating from the Shabbat candles warms a Jewish home on Friday night. And, in fact, one of the reasons we light the Shabbat candles is to delight or take pleasure in the Sabbath (oneg Shabbat, in Hebrew).
The reason the candles are considered a delight is not only for their beauty, but because they provide light for the house, helping folks not to stumble or get injured, and bringing shalom bayit, peace into the home.
The candles are so important that Rabbi Joseph Karo, author of the Shulchan Aruch, the most important book on Jewish law, ruled if a family was so poor it didn’t have money to purchase everything needed for Shabbat –– challah, wine, etc. –– it should still purchase candles.
Traditionally, women light candles, and if there is no woman present a man does.
Most people light two candles, relating to the two ways we are commanded to observe Shababt (shamor, to guard the Sabbath day (Deuteronomy 5:12), and zachor, to keep Shabbat (Exodus 20:8)).
One could light more than two. Some women light seven, which correspond to the days of the week. Some light 10, which correspond to the 10 commandments. Others light the initial two, plus one more for each of their children.