Ok, so it turns out that I need to explain the story of Martha and Mary. First, the passage (from Luke):
In the course of their journey he came to a village, and a woman named Martha welcomed him into her house. She had a sister called Mary, who say down at the Lord's feet and listened to him speaking. Now Martha who was distracted with all the serving said, 'Lord, do you not care that my sister is leaving me to do the serving all by myself? Please tell her to help me.' But the Lord answered: 'Martha, Martha,' he said 'you worry and fret about so many things, and yet few are needed, indeed only one. It is Mary who has chosen the better part; it is not to be taken from her.'
Ok, so let's look carefully at what Jesus said:
Martha, Martha, you worry and fret about so many things, and yet few are needed...
First, we have reference to the physical labor. Martha has chosen not to listen to Jesus because there is much work to do, yet Jesus points out that most of it is unnecessary work. Here Jesus is plainly speaking about practical matters; it is clear (to those who have ever entertained guests) that Martha is busy running around making sure that everything is as it should be (according to social expectations) when to satisfy the goal of happy and fed guests, very little work is actually necessary.
Lest this point is lost on anyone who has never really entertained guests (or been a guest themselves), let me explain. Hosts tend to build up expectations of how well everything should go, and worry that things are not going as they should. As a result they spend a very long time preparing (cleaning, getting things ready, arranging things, etc), and when the guests arrive they serve food, make sure that beverages are pored, etc. Of course Judea 2,000 years ago would be different from a modern social visit, but it is human nature to fret and worry. It would not be at all surprising if Martha was occupying herself with busywork just to give herself the emotional safety net in case anything should go wrong that it didn't go wrong because she slacked off. She wouldn't be the first host to do so.
And recall that Jesus was something of a local celebrity — even at the time no ordinary person. Entertaining guests that one doesn't know generally involves more work than entertaining friends.
So, Jesus is pointing out to Martha that there is no practical need to go to all of the trouble that she's going to. One should give guests some food (and of course there is the occasional ritual such as washing someone's feet), but what is necessary is small in comparison to what Martha is doing. She is doing work, but even for practical, physical ends it is more than is required.
...indeed only one.
Now Jesus switches to the religious content. Here, simply enough, is the statement that all social amenities are of lesser importance than religion. Pleasure, comfort, etc. are not necessary things in comparison to salvation, and when a person has to decide between listening to the words of God and providing for physical comfort, they are not wise to choose physical comfort.
It is something to remember when reading the new testament that Jesus always held his presence to be something special — a unique event which brought with it a temporary suspension of many lesser rules (customs, never moral rules). One of the pervading themes of the bible is that Jesus had something to say, it was important, and he wouldn't be saying it for all that long so people had better listen.
It's always difficult to look back through history — things are always emphasized in modern day which weren't in the past. People growing up in the 20th century are familiar with Jesus (if they have had any christian upbringing) as an all pervading figure. He's on virtually every page of the gospels, and in the overwhelming majority of paragraphs. People with anything of a Christian upbringing are used to the idea of hearing what Jesus said every Sunday, if not more often. Yet this nothing like how the people of Judea experienced Jesus. To them he was something of a whirlwind — he would come visit a town, heal the sick, perhaps work some miracles, preach, then leave. He was never in one place for all that long because he was on a mission to spread the good news. (this is all a bit general, and of course there were times during those 3 years when Jesus spent more time in one place than in others, etc.)
The chance to hear Jesus preach was not a repetition of the weekly grind of lifeless ritual. It was in many cases a once in a lifetime chance to hear someone who was giving away the correct explanation of what life is all about. Martha and Mary would likely not have another chance to hear Jesus while he was alive.
There is therefore something of a tendency on the part of some modern readers to want to over-generalize everything in the gospels. It is often presented as if it were written for us as we often now use it — a reference manual — not as it actually was — an account of the strangest thing that ever happened. Jesus was a flesh-and-blood man who dwelt amongst us, died, and was buried. Therefore the time while he was walking on the earth is distinct from the time when he wasn't, and an awful lot of things which applied to him stopped applying when there was no him around for them to apply to.
In this story, for example, it's by no means clear that there's any direct modern analog to the dilemma facing Martha and Mary. In the story Martha will not give up what are essentially chores in order to listen to something momentary of tremendous importance (indeed, something of all-importance). There is nothing in modern life which is a singular moment of such similarly tremendous importance.
One should draw the useful lesson that if one is suddenly exposed to a world-altering revelation about the very nature of life, one should not put it off even if the telephone is ringing. It's very far from clear that there's anything more practical than that to be directly learned from this passage. The details look to be important, here. There's nothing which suggests that the temporary nature of Jesus' preaching was not the reason why minor practical matters should be left unattended. It is certainly the most obvious and reasonable explanation — the one which most accords with the rest of the bible and common sense.