Minus is another lost soul who feels unloved by his father and is sexually confused and frustrated. He is bewildered by his sister's actions and spends his whole time brooding or running around in a state of confusion. Karin and Minus commit incest in the depths of a shipwrecked hull. This act sends her over the edge and he close to it.
The other characters are older men. Martin (Max Von Sydow) is Karin's husband. He genuinely loves Karin and is helplessly unable to reach her and be of any use. He is the least interesting because he is the only character not to undergo any sort of crisis. David (another Bergman regular- Gunnar Bjornstrand) is Karin and Minus' father. His children are critical of him. He doesn't feel much love for them. He is cold and self-obsessed and indifferent and is often away on his journey as a pseudo poet/ novelist. He has a lack of understanding of his children's needs and Martin is critical of him for using their experiences as fodder for his fiction and diaries.
What saves David and makes him a compelling figure is his breakdown that occurs offscreen in Switzerland. He tries to kill himself (offscreen) by driving off a cliff face, but miraculously survives because his car stalls at the eleventh hour, and two wheels are left dangling off the precipice. Because of this near death experience he has a sudden genuine, rapturous love for Martin and his children.
This new found love isn't shared with others until the end of the film. Karin has been taken off to hospital and presumably an asylum by helicopter. Martin leaves also, no doubt feeling useless and bewildrered. Minus has tried to avoid his father because of the understandable guilt he feels because of the incest. He reaches out to his father, helplessly, and announces that he cannot live in this world any longer. He must have some comfort. Is there a God? This is the exact moment when David has to help his son, probably for the first time. He tells him that 'love exists for real in the human world', and as a consequence Minus feels reassured that God, if 'love and God are the same', surrounds and provides comfort to Karin.
The ending of the film has been criticised as being unconvincing in its attempt to provide hope and reconcile Minus and David. David's words do come across as being a bit forced. Bjornstrand is very solemn in his simple explanations, and this is easy to mock. There is a camera pan towards his face that emphasises the solemnity of the occasion. Bergman himself is said to regret the ending, that it makes the film belong to the decade of the 50's rather than the 60's. Yet, despite all this, the message is still beautiful in its own way, even though it is simplistic. It is this new found love in his heart that will enable David to go on living. And it is a fantastic thing that Minus can share in the authenticity of it and have his own obliterated hope renewed. Unfortunately the final words spoken in the film (from Minus) are: 'Papa talked to me.' So much better if we were just left with no words, just that boyish enlightened face!