Stephen had been performing signs and wonders in the name of Jesus Christ, and because of this, was brought before the Sanhedrin. There he delivered a long speech about how Jesus was the fulfillment of all that their ancestors had said and done.
The members of the Sanhedrin were furious. They dragged Stephen outside the walls of Jerusalem and stoned him to death. (Luke notes that a young man named Saul was part of this.)
Since the fourth century, the day after Christmas has been the feast of the first martyr, St. Stephen.
It may seem strange to celebrate a death just one day after celebrating the birth of Christ. But the Church put this feast her on purpose: To teach all Christians that they stake their life on this child born in Bethlehem.
- Little Blue Book, Diocese of Saginaw