The lighting of the candles is not only the first act of welcoming Shabbat, in which the members of the household receive its sanctity into their midst.
It also expresses the essence of Shabbat itself, the penetration of the light of this special day into mundane reality.
For, on the surface, this day is no different from any other.
The material context of our lives is outwardly unchanged.
Yet it is possible to illuminate this outward reality in a way that gives everything about it a different character and meaning.
This is the sense of the lines we sing in honor of the Shekhinah/Shabbat/the bride:
"Thy light has come;
Arise, O my light;
The glory of the Lord
Is revealed upon thee."
–Rabbi Adin Steinsaltz
From Teshuvah by Rabbi Adin Steinsaltz