As a progressive, post-theist Christian, I find that two ideas capture the meaning of Christmas.
First, Christmas acknowledges that every person, every aspect of the cosmos, is embraced by the light. That light is also called God, Buddha, or ultimate reality. By any name, the light that embraces us nudges or lures one in the direction of more abundant, loving life. The story of Jesus' birth dramatizes that embrace and invites its hearers to live more deeply into the mystery of being embraced by the light.
Second, Christmas by inviting us to live more deeply into the mystery of being embraced by the light invites one to recognize and nurture the capacity for being loved and loving that is an integral element of every human. Jesus, embraced by the light, experienced such a powerful awakening of his capacity to love and be loved that people described him as both fully human and divine.
So, during these twelve days of Christmas, welcome the light's embrace and then respond by deepening and broadening your capacity to love and be loved, i.e., to live and to walk ever more fully in the light.