I have only watched it one time but from other Christians in the past have said about it, I understand they feel it presents Christian values in a down-to-earth atmosphere that people living today can relate to. That it presents an idea of how a family can live its life as a Christian family and be normal within contemporary society.
I saw an interview with the guy that plays the father in the movie. He was saying that he gets fan letters in large volume of viewers asking him for advice on having a relationship with God. Many of them, from what he said, didn't see him as an actor but more of a "tv pastor" who could offer legit religious guidance when not on the show. It was in a magazine and years ago, so I don't have a link or reference. I remember he was taken aback at the idea he was viewed as something other than an actor playing a part.