I was thinking about the battle between light and darkness in Fanny & Alexander and especially of how you have many dark scenes that could realistically occur contrasted with the need for magic to save the children and restore a joyful mood.
I think maybe even the Ekhdahl family scenes shows the darkness of the various relationships - you have the (even if its condoned) adultery in the relationship of Gustav Adolf and Alma (perhaps she is afraid of losing him if he does not have extra-marital affairs?), the bitter marriage of Carl and Lydia with its insults from Carl and submissiveness from Lydia as well as its raising of the issues of money, and the marriage of Oscar and Emilie which while it seems fine deals with the issue every couple must face, that of the death of their partner (or their death leaving their partner alone). Even the relationship between Helena and Isak suggests love that might have been fulfilled without societal pressures and it is left to the audience to wonder about that: did Helena marry before she met Isak or did she know him but married her husband for different reasons such as financial (perhaps shown by her talk of her son's finances) religious issues, family pressure etc?
So even in the happier scenes I think Bergman is exploring all the various problems that can occur in relationships before focusing more exclusively on the marriage of Emilie and the Bishop. It seems to me that in the post-Christmas scenes following Gustav Adolph and Maj then Alma, Helena and Isak, and Carl and Lydia that the intention of showing them is not just to round out the family but also to suggest that the film could follow any one of these relationships to explore its themes, and that it is an event like the death of Oscar and the entrance of the Bishop that throws the issues into stark contrast and shows that for all their problems, the Ekhdahl family is a loving one.
I like Bergman for this because it seems better to show the problems than presenting a purely lyrical, wonderous Christmas - it made me feel the situation was more realistic, and that how wonderful something is can be subjective, but if this is the case then also how bad things are can also be subjective and will pass. I'd like to think that the reason for the Christmas scene (as well as for it being so long) is to provide not just Fanny and Alexander but the audience with a wealth of moments that they can cling to when the film turns dark at the Bishop's house. I think that Bergman is illustrating the need for such moments to pull us through the dark times, and that without them people would be less able to cope with the sometimes harsh realities of life. This rememberance I think is also related to the need for a healthy imagination as shown by Alexander inventing his stories and the Bishop trying to stop them, and thereby I think Bergman suggests the Bishop is trying to stop Alexander from having a life in his own head (with his thoughts of home and his interpretations of life in the form of his stories) now that he has full control over his external existence (perhaps this may be a comment by Bergman at the power of organised religion over peoples ways of thinking?).
The problems do seem very probable and realistic (the Ekhdahl family's problems and the relationship between the Bishop and his new family with the use of religion as a controlling force and the caning of Alexander) and I'm not sure what to make of the resolution of the darkness by magic. I think this is a good thing, giving us different views depending on who we are as audience members and what we are feeling at that particular time.
I know in my case that if I'm feeling in an 'up' mood whilst watching it the use of magic seems like a vindication of imagination and the supernatural over the oppressiveness of real life and situations that are almost impossible to overcome - its the literal expression of an imagination that has been so stifled during the course of the Bishop-centred part of the film.
If I'm in a 'down' mood it gets me to wondering if maybe a magcial act was the only way Bergman could see to get the children out of the house, and that the Ismael character seems more creepy and perhaps vindicative in the use of the power of Alexander's hatred to start the fire. It makes me think that maybe Bergman could not see a realistic avenue of escape for Emilie and the children, especially clear to the audience after the ineffectual attempts of Gustav Adolph and Carl to talk to the Bishop.
However, I think the tone of the film is happy and that my 'down' interpretations while possible, are not likely given the amount of emphasis placed on imagination and magic or supernatural events throughout the film, and I find hope that in Alexander's darkest moment in the attic the vision of the children that, while it is disturbing, shows that Alexander is still not mentally beaten by the Bishop. And when Isak reads the story, Alexander's imagination is allowed freedom again and produces one of the finest dream moments of the film, showing that he will be scarred by the memory of his experience with the Bishop, mentally rather than the maid's (Harriet Anderson's) physically scarred hands, but has come through the ordeal. It is interesting to contrast this with Through A Glass Darkly where the visions lead the character into madness.
I think this shows how important the television version is compared to the theatrical one. A lot of important events are removed and that compromises the above interpretation, with the cutting down or removal of almost all the imaginings of Alexander and his interactions with Fanny either with the other children at Christmas with the magic lamp, or with their attempting to kill the Bishop. It shows that whilst Alexander is the primary focus where the imagination is concerned, Fanny is more than willing to be a part of his stories and imaginings, even if it is left unclear what she sees of the father's ghost, for instance.
I would definitely agree with you John about there being no problem with the five hour version but the three hour seems to have superfluous bits, perhaps it was Bergman's way of subconciously getting the audience to want to see the longer version!
I'm not sure how far off track I've got with this interpretation but it has been very interesting to think it through!