In Part 1 Chapter 5 of The Stranger, what would be the overall theme/message in the chapter?

The reader is further struck by the totality of the theme of Meursault's indifference and apathy during this part in his life when he agrees to marry Marie. Many times, Meursault will make a decision based on the fact that he sees no reason not to act in a certain way though he does not see a reason to either. He will get married if Marie wants to and he is annoyed that she questions his reasons when it is her idea.