The purpose of lighting two candles is to create balance in the middle column as Shabat opens.
On Shabbat we recognise that the home is a sanctuary. The lady of the house welcomes Shabat by lighting the candles, and reciting a short prayer. Female energy is considered to be the purest link to Divinity.
The Shabbat candles are an invitation to the Divine Presence, the Shechinah שכינה to enter the home.
The lady of the house is considered to be a conduit for light and peace, and to connect Malkut מלכות and the home with the Divinity of the upper nine Sephirot.
On lighting the candles, the lady of the house recites a prayer to welcome the light of Shabat.