It was written by nice screenwriter Mike Rich, who also wrote the nice "Finding Forrester," "The Rookie" and "Radio." You will note that "nice" doesn't necessarily mean "good." It means pleasant and unassuming. You will not have to think very hard about anything while watching a "nice" movie, nor will your preconceived notions be challenged. There is nothing wrong with most "nice" movies -- nor, in many cases, is there anything right with them.
"The Nativity Story" is bland in that way, though it has details that give it some honest respectability. The director, Catherine Hardwicke, has made far edgier films in the past ("Thirteen" and "Lords of Dogtown"), and you can see her wanting to inject realism into this project, too. Little details, like two young boys' amusing reaction to witnessing a circumcision, or the pain in Elizabeth's face when she gives birth to John the Baptist, remind you that Hardwicke is accustomed to stories grounded in modern realities rather than glossy religious traditions.
Rich's screenplay takes what little we know from the New Testament and expands to give Mary, Joseph, and the others backstories. Mary (Keisha Castle-Hughes) is a young, carefree girl whose parents are cheesemakers. (And as we know from Monty Python's "The Life of Brian," blessed are the cheesemakers.) With no input on the decision whatsoever, she is betrothed to Joseph (Oscar Isaac), a decent young man from her village with whom she has had little prior contact. Now they are semi-married, called spouses but forbidden from doing "that which leads to families," as Mary's dad puts it, until the marriage is finalized.
This restriction makes things a bit awkward, as you know, when Mary finds herself pregnant. The biblical account is retained (including the dialogue, when possible), with angels visiting Mary and Joseph to explain their roles in God's plan. Mary goes to visit her kinswoman Elizabeth (Shohreh Aghdashloo), who is miraculously pregnant, too, having conceived despite being old and infertile.
Meanwhile, we get a rather goofy account of the Magi, three Eastern astrologers who see the signs in the sky and follow the star to Bethlehem. They're portrayed as normal, down-to-earth fellas who kid one another and act like buddies. This is probably accurate enough, but it's a jarringly different tone from the seriousness of the rest of the movie. Mary acts like a religious icon; these guys act like average joes.
Yes, there's something about Mary: she's boring. Keisha Castle-Hughes, just 15 when the film was shot, has trouble hiding her Australian accent (everyone else uses a generic "Middle East" inflection) and renders every line flat and emotionless. Joseph and Elizabeth feel like fully realized characters, but Mary appears just as she does in paintings: two-dimensional, kind of pretty, and entirely without substance.
I think the film serves its purpose well enough, if that purpose is to be a modest, mildly uplifting Christmas story. Considering most Christmas movies have nothing to do with Jesus whatsoever, "The Nativity Story" should be a welcome surprise for Christian families. Which doesn't mean it's very good as an expression of art, only that it's ... you know ... "nice."