The last line of The Stranger relates to Meursault's epiphany regarding the universe. He has come to believe that reality is as indifferent to human actions as he himself is. There is no moral order. There is no inherent meaning underlying existence. Things often happen for no reason whatsoever, and it is therefore futile to try to impose meaning on what is ultimately a meaningless universe. The last line is as follows:
For all to be accomplished, for me to feel less lonely, all that remained to hope was that on the day of my execution there should be a huge crowd of spectators and that they should greet me with howls of execration.
This viewpoint is in opposition with that of every other character in the novel. Marie prizes social institutions such as marriage. The magistrate and the priest insist that there is a benevolent God who gives the world meaning and therefore grants significant meaning to human activity. The lawyer expects that there is a reason behind Meursault's murdering the Arab man on the beach. With his ultimate condemnation from the court, Meursault is marked as a social menace, though less for committing murder and more for his existential indifference.
By wishing for an audience of hateful spectators at his execution, Meursault is showing that he is content with being an outsider. Now that he believes the universe is as indifferent as he is, he comes to view this reality as gentle and comforting. He does not need society's validation in order to be happy, and he revels in that fact.