From The King Center web site:
The Martin Luther King, Jr. Holiday celebrates the life and legacy of a man who brought hope and healing to America. We commemorate as well the timeless values he taught us through his example — the values of courage, truth, justice, compassion, dignity, humility and service that so radiantly defined Dr. King’s character and empowered his leadership. On this holiday, we commemorate the universal, unconditional love, forgiveness and nonviolence that empowered his revolutionary spirit.
We commemorate Dr. King’s inspiring words, because his voice and his vision filled a great void in our nation, and answered our collective longing to become a country that truly lived by its noblest principles. Yet, Dr. King knew that it wasn’t enough just to talk the talk, that he had to walk the walk for his words to be credible. And so we commemorate on this holiday the man of action, who put his life on the line for freedom and justice every day, the man who braved threats and jail and beatings and who ultimately paid the highest price to make democracy a reality for all Americans.
The King Holiday honors the life and contributions of America’s greatest champion of racial justice and equality, the leader who not only dreamed of a color-blind society, but who also lead a movement that achieved historic reforms to help make it a reality.
ETA: Short but information packed biography of Coretta Scott King here.