Louis is old and bitter about his life and his family. He sees them as a "nest of vipers," all trying to get an inheritance from him while pretending to be concerned about his health. Of all the relatives, he perhaps has the deepest connection with Janine, who he describes at first in very negative terms:
...until the day of her death, Janine will be a woman "in the know," repeating everything she hears... trotting out second-hand views about this, that, and the other, and not understanding a word.
He sees her as a woman without a personality or ideas of her own. In his mind, Janine is a woman who does not experience individuality, but instead receives her opinions and ideas from others; she is "putting on an act" in order to be seen as intellectual and worldly. However, despite the damage done to her own mental state by the family, Janine retains some individual intelligence, and is eventually repulsed by the family's actions in regards to herself and to Louis.
All our strength was employed in keeping out eyes fixed on material things,while Grand'pa... I wonder whether you will understand what I mean when I say that where his treasure was, his heart was not?
(Mauriac, Vipers' Tangle, amazon.com)
In the end, Louis reconciles with Janine; they find in each other parts of the individual that they were missing. Alone of the family, Janine stays with Louis as he dies, and comes to realize that his fortune was not important after all. Instead, the conversations she has with him on philosophy and faith change her for the better, and as she realizes this, Louis too comes to realize that his life was not in vain, and that he affected someone -- Janine -- for the good.