This is an ancient feast that goes back to the fourth century. It used to be called the Purification of the Blessed Virgin Mary (referring to the legal purity required of Jewish women after childbirth). But today the focus is a little more on Jesus the Lord.
In the Gospel, Simeon proclaims that Jesus is a "light of revelation to the Gentiles." So the theme of light is a major part of the liturgy. It begins with the blessing and lighting of candles, and a procession through the Church. Christ is the light of the world.
Through the years the feast began to be celebrated as a special feast for consecrated persons. It's a day when we renew our vows and rededicate ourselves to the Lord's service. Pray for all religious, that we might be like the wise virgins in the Gospel, always ready with our lamps lit to welcome the Lord.