In Chapter II of The Stranger, Meursault says:
I remembered it was a Sunday, and that put me off; I’ve never cared for Sundays.
In Chapter III, Meursault is prompted by Raymond to write a letter that may be used to lure his Arab (Moor) girlfriend back to him. Meursault responds:
I kept silence and he said it again. I didn’t care one way or the other, but as he seemed so set on it, I nodded and said, “Yes.”
In Chapter V, when asked by his boss if he'd prefer moving to Paris for a job promotion, Meursault responds:
I told him I was quite prepared to go; but really I didn’t care much one way or the other.
In Part II, Chapter II, Mersault finally starts to reflect on his life once in prison. He says:
THERE are some things of which I’ve never cared to talk. And, a few days after I’d been sent to prison, I decided that this phase of my life was one of them.
Later, in Part II, Chapter V, Meursault reflects on death:
And, on a wide view, I could see that it makes little difference whether one dies at the age of thirty or threescore and ten—since, in either case, other men and women will continue living, the world will go on as before.
So, Meursault doesn't care about that which most of the culture cares about: Sundays, revenge, job promotions, prison, and even death. As an absurd hero, Meursault is either in denial or in a state of repressed anger about the importance of these events. In short, Meursault hates death, loves life, and scorns the gods. He does not see any religious importance to the ritual of Sunday, the point of menial labor, or the fear of death--for he, like his mother, is ready to live his life over again just the way he lived it in the first place--with no guilt or regrets.