I think this is a beautiful tradition and want to learn all I can about it. However, is it actually written in Torah to light a candle, or does it only say to observe the Sabbath and keep it holy?
The most precious things in life are said silently. Those who need to understand—those who are not strangers, those who hear the words from the inside—understand. Similarly, with Shabbat: when G-d gave it to us, He did not need to spell out its most precious customs.
Take a look: whenever the Torah mentions Shabbat, it always seems to be assuming that we know what it's talking about. The Torah admonishes us to "keep the Shabbat" and "remember the Shabbat." We are to rest on the seventh day from the work of the other six, and so are our servants and domesticated animals. Don't make a fire, There's a strong implication that we don't build tabernacles on Shabbat. From all this we can figure out a lot of things that we are not supposed to do—such as anything that's involved in building a tabernacle. But regarding what we are supposed to do, not a word. It seems that the Moses crowd just knew--perhaps by intuition, perhaps by tradition.
The prophet Isaiah, however, does elaborate a little on what Shabbat entails. His audience was, after all, a little more distant from the light of Sinai--and so needed things spelled out. He says, "If you restrain your foot because of the Sabbath, from performing your affairs on My holy day, and you will call the Sabbath 'a delight' and G-d's holy day 'honored'…."
So, Shabbat is a day we are to honor and delight in. But how do you honor and delight in it? Apparently, Isaiah's audience needed no further explanation. But in Talmudic times, things got to the point that it was necessary for the rabbis to spell out every word: you honor the Shabbat with clean clothes and delight in it with fine food and drink.
Now, here's where the Shabbat candles come in: Have you ever sat down to a delicious meal in the dark? Not too much fun. Who knows what that fork may end up piercing? But, worst of all, even the finest cuisine becomes a drab affair when you can't see the colors, textures, and forms of those delicious morsels. We are visual creatures, and even our capacity to derive pleasure from our food is tied to our visual experience. "A blind person," the rabbis say, "is never satisfied from his food."
And so, as long as Jews were interested in "calling the Shabbat a day of delight," they must have had a lamp lit for the nighttime meal. It had to be lit beforehand, since--as we are told explicitly--we cannot create a fire on Shabbat. And since it is the woman who generally takes the responsibilities of the home, presumably, she took the responsibility of the lamp.
Yet, it seems that later down the line there were Jews who felt okay skimping on the visual experience. Maybe the cost of oil was escalating. True, you can't eat a meal without light and enjoy it. But people said, "Let's just eat it that way anyway and say we did." Now, if people don't want to enjoy, it's hard to tell them, "You must enjoy!" But sitting in a dark home all Shabbat creates other problems. Shabbat is meant to be a day of peace and harmony. A dark house, with people tripping over every unseen obstacle and falling all over each other is not conducive to peace and harmony.
So, at some unspecified point in history, for the sake of Shalom Bayit (family harmony), the spiritual leaders of the generation made a distinct requirement that every home must have a lamp lit before Shabbat in every room where people may walk and bump into things. They declared that anyone who would be careful with it would be blessed with children who would be Torah scholars, as the verse states, "For a mitzvah is a lamp, and the Torah is light." They interpreted this to mean that through the mitzvah of the lamp would come the light of Torah.
Nevertheless, the principal lamp is the one that shines over the Shabbat meal. The other lamps can be fulfilled today with electric lights, but the light by the meal should be a burning flame—unless that's just not possible (e.g. in a hospital).
Now you can see that the Shabbat lamp, even though it is technically a rabbinic institution, has always been an integral part of the Shabbat. Our tradition is that Abraham and Sarah kept the entire Torah even though it was not yet given. They knew the Torah from their understanding of the inner mechanics of the universe. Sarah lit the Shabbat lamp, as did Rebecca, Rachel, and Leah. It's reasonable to believe that at no time in our history did a Friday night pass without that light. And with that light we will enter into the "day that is entirely Shabbat and rest for eternal life." May that time come sooner than we can imagine.
Rabbi Tzvi Freeman