If there is no immortality, there is no virtue. ... Without God and immortal life? All things are lawful then, they can do what they like? - Fyodor Dostoyevsky

Existentialism isn't so atheistic that it wears itself out showing that God doesn't exist. Rather, it declares that even if God did exist, that would change nothing.

I have never in my life met a man like him for noble simplicity, and boundless truthfulness. I understood from the way he talked that anyone who chose could deceive him, and that he would forgive anyone afterwards who had deceived him, and that was why I grew to love him.

I sometimes have moments of such despair, such despair … Because in those moments I start to think that I will never be capable of beginning to live a real life; because I have already begun to think that I have lost all sense of proportion, all sense of the real and the actual; because, what is more, I have cursed myself; because my nights of fantasy are followed by hideous moments of sobering! And all the time one hears the human crowd swirling and thundering around one in the whirlwind of life, one hears, one sees how people live — that they live in reality, that for them life is not something forbidden, that their lives are not scattered for the winds like dreams or visions but are forever in the process of renewal, forever young, and that no two moments in them are ever the same; while how dreary and monotonous to the point of being vulgar is timorous fantasy, the slave of shadow, of the idea...