There is a rabbinic mitzva to light a candle to honor Shabbat. There are three reasons for this: 1) to honor Shabbat, as a banquet without light is of no significance; 2) for oneg Shabbat, because one who cannot see his food does not enjoy it; 3) to bring shalom bayit (peace in the home), because one who cannot see his furniture and belongings trips over them and gets angry and irritable. It is so important to have light at the Shabbat table that the Sages stated that one who does not have enough money to buy a candle should go door to door begging for charity in order to buy it (SA 263:2).
One who has only a bit of money should first buy bread so he does not fast on Shabbat. After that, if he still has money left, he should buy a candle, and only then, if he can, should he buy wine for kiddush. This is because one may make kiddush over bread if necessary, and the light allows him to honor and enjoy Shabbat. It is more important to light a candle to honor Shabbat than to beautify kiddush with wine (Shabbat 23b; SA 263:1-2).
The Shabbat candles give profound expression to the essence of Shabbat. One mired in darkness cannot find what he is looking for; he stumbles over his furniture; his whole home seems chaotic to him. But the moment he lights the Shabbat candles, peace comes to his home. He understands that his furniture is there to serve him, and his belongings are all where they belong. Thus he is able to enjoy Shabbat at his festive meal. Similarly, when we look at the world superficially, it seems full of strife and war, hopelessly divided and conflicted. Each side thinks that only when it succeeds in getting rid of the opposition will it be able to rest, and thus the conflicts endlessly continue. But if one thinks a little more deeply and examines divine providence, the darkness disappears and the divine light is revealed. He realizes that the opposing sides actually complement one another, and there is a hand directing and leading the world toward perfection. Out of all the troubles and afflictions, redemption and comfort will emerge (see above, 1:15).
The Shabbat candles, which bring peace to the home by adding light, thus allude to the repair of the world that comes about by increasing the light of Torah and faith. This is the goal of Shabbat – to add the light of faith and Torah to the world. It seems that this is the reason for the great love that all Jews have for the mitzva of Shabbat candles: It alludes to the overarching goal of the Jewish people – to make peace by adding light.
With this in mind, one can understand the Sages’ statement that one who is meticulous about lighting Shabbat candles will be privileged to have children who are Torah scholars (Shabbat 23b). For by occupying oneself with the light of Shabbat, one merits having a child who adds the light of Torah to the world. Accordingly, after lighting the Shabbat candles, many women customarily pray that their sons become Torah scholars.
The Sages state in God’s name: “The glory of Shabbat is its candles. If one observes [the mitzva of] Shabbat candles, I will show you the candles of Zion…. It will not be necessary for you to use the light of the sun to see; rather I will provide illumination for you with My glory…. In the future, the nations will walk by your light…. Why do you deserve all of this? Because of the candles you light for Shabbat” (Yalkut Shimoni, Beha’alotekha).