What religious symbols or concepts play an important role in Crime and Punishment by Dostoevsky?
The first symbol of religion to be introduced is the color yellow when Raskolnikov goes to the room of "the old woman":
there hung flapping on her shoulders, a mangy fur cape, yellow with age. ... The little room ... with yellow paper on the walls, ... old and of yellow wood ... prints in yellow frames ...
Yellow is a multilayered and double-pronged symbol that is very intricate and lays the groundwork for later important religious concepts and symbols.
It is multilayered because yellow symbolizes (1) religious Truth and Purity in a similar fashion that white does; (2) degradation and old age; (3) death and corruption; (4) sin. It is double-pronged because it represents both Alyona Ivanovna and Raskolnikov. For Alyona Ivanovna, yellow symbolizes the sanctity of Life, her old age, and her impending end (as it foreshadows that as well). For Raskolnikov, yellow symbolizes his degradation ("he was very weak; for two days he had scarcely tasted food"); his spiritual nature; and his sin.
Another important symbol is hand washing. Shakespeare used this same symbol religious symbol in Macbeth. This symbol is also a Biblical allusion to the ritual hand-washing Pontius Pilate preformed when he removed the guilt for Jesus's crucifixion from his own soul and left it with the crowd. Here, the symbol points to the same representation: an attempt to remove guilt and anguish. It is first introduced with Marmeladov and Katerina Ivanovna but carries throughout. It is equally applicable to Raskolnikov either as washing or being unwashed:
He rummaged under his pillow and picked out amongst the linen stuffed away under it, a worn out, old unwashed shirt.
An important religious concept is that of forgiveness and it applies to Raskolnikov and all the principle characters. This aspect of multiple applications is an echo of Philip Sydney's theory of mimetics in which every possible experience with an idea, or concept, either good or bad, is presented in the narrative: each character, including Dounia, has a unique experience relating to forgiveness. Of course, it applies in the most profound way to Raskolnikov:
the blow fell on the very top of her skull. She cried out, but very faintly, ...