It's difficult to choose a representative film from the entire Ingmar Bergman's filmography. Each film deserves a comment because it's like a piece of art in its own.
I chose "Skammen" because I saw it recently and because I think the message -although being a 1968 film- is still valid. The subject is quite simple: a couple is surprised by war, which changes forever the existence of the two people. We can discover their real feelings and their real values.
We can find shame in more levels.
First, husband's shame for not being able of giving a child to his woman. He's also an extremely coward man in the first half of the movie, he feels shame also for that.
Second, wife's shame for not being a mother -she feels frustrated. She's shameful also because she has betrayed her man with an important man of their country's army.
Third. They both feel shame because they pretend being friends of this man, who saves them from tortures and jail. (They're actually accused of being traitors, in expressing other political opinions.) As a compensation, that man come to their home whenever he wants and take advantage of his position for becoming a woman's lover. The husband lets things going like this, it's the price he pays for a kind of freedom...
Fourth. Shameful is of course war and life during it.
Bergman makes a flawless movie, he studies people as they are. Without big budgets and huge sets. A simple film, deep, superbly photographed in black and white.