Our sages tell us that the Shabbat candles that Rivka lit burned throughout the week, giving Yitzchak and Rivka the feeling of the sanctity of Shabbat even after Shabbat.
Every mitzvah we perform brings light into the world, as it is written: «The mitzvot are like a candle and the Torah like a lamp,» but we don’t always see or feel this light. Shabbat candles are special because we can see their light, the light of the mitzvah, shining in our homes. When we observe the peaceful flickering of the Shabbat candles, we understand and feel the special holiness that comes with this mitzvah.
Can you imagine how wonderful it would be if that holiness lasted all week? That's exactly what Rivka and Itzjak felt. That's exactly what happens in our homes.
Shabbat candles bring us feelings of joy and peace. Even though we may be very rushed and busy on some Fridays, our homes suddenly become calm as soon as we light the Shabbat candles. And this light remains even after Shabbat ends. Although we cannot see the light during the week, like Rebecca and Isaac, it is still there, making our homes joyful and peaceful.
Rivka's Shabbat candles, our matriarch's, brought that sanctity when she was only three years old. This is a lesson for all Jewish girls.
As soon as a girl turns three, or as soon as she understands the meaning of lighting candles, she should light her own candle. This will bring light and holiness to her home and the world.
Extracted from Please tell me what the Rebbe says.