TODAY'S MUST-SEE

"CNN Presents: After Jesus — The Earliest Christians," 2 p.m., CNN; reruns at 5 p.m.; also, Saturday and Dec. 24. At first, this excellent documentary says, no one intended Christianity to be a separate religion. The goal simply was to adjust Judaism. Later, fresh debates grew. Roman retribution began, with Christian leaders facing brutal deaths. Then, in A.D. 312, Emperor Constantine, began converting to Christianity. He was a flawed Christian, this film says. He continued to practice paganism and ordered the deaths of his wife, his son and others. His mother, Helena, was more committed. She traveled to the Holy Land and ordered the building of grand churches. Constantine brought an era of tolerance. It would be a key step in a religion that now reportedly has 2 billion believers.

OF NOTE

"Christmas With the Mormon Tabernacle Choir," 7 p.m., and "Great Performances: Renée Fleming: Sacred Songs and Carols," 9 p.m., PBS. The glorious voice of soprano Renée Fleming is featured in both seasonal specials. The first is new from Salt Lake City; the second is a rerun from last year that was taped at the Mainz Cathedral in Germany.

"Bones," 7 and 8 p.m., Fox. The first rerun has Brennan's former professor (who is also her former lover) visiting and becoming interested in her new case. The second has the team being quarantined at Christmas time.

"How I Met Your Mother," 7:30 p.m., CBS. In this rerun, a bitter Ted hurls such an evil insult that everyone feels bummed.

"Lance Armstrong: Running for Life," 8 p.m., TLC. Forget this documentary's title. The film actually traces three people taking their first crack at the New York Marathon. Armstrong, the former world cycling champion, is one, but the others are even more interesting. One is a tough soldier who lost both legs in Iraq and uses a hand-powered cycle; the other is a teacher, fresh from treatment for cancer.

"Day Break," 8 p.m., ABC. Hopper thinks he might have found someone else who keeps reliving this awful day.

"Medium," 9 p.m., NBC. This rerun borrows a "Day Break" twist: Allison relives a day in her dreams, adding clues along the way.