The hobbits traveled eastward, coming across new companions, including Tom Bombadil, Aragorn and Glorfindel. Simultaneously, Black Riders repeatedly attempted to capture Frodo. Therefore, throughout their journey, there was a leitmotif of opposite extremes: light and dark, and black and white.
According to Strider, the Nazgûl is dependent to nighttime. These antagonists hunt by perceiving shadows and lifeblood. Hence, the night is of danger, and the day is of safety, to the protagonists. Demonstrated at Weathertop, fire was ignited for protection. They were desperate for light; but the Ring itself leads to the dark.
The Ring alludes the power of Satan, since it grants mortal desires for perfection, tempts seekers to undertake deadly sins and become a god—a megalomaniac like Lucifer that thirsts supremacy. It has the capability to turn the wise into a fool (even Gandalf refused to touch the Ring).
Frodo, then, is being pulled into the darkness—both to his fate/destination, and repeatedly in his expedition. Blackness enabled the Nazgûl to terrorize the Inn in the Bree, the camp in Weathertop, and the Ford of Bruinen in Rivendell. The absence of light still awaits him.
Black symbolizes wickedness and sinfulness; white symbolizes virtuousness and righteousness. Even if the characters could not comprehend the Black Riders, they still bring fear, through its uncomforting and demonic colors. In the other hand, Asfaloth, Glorfindel’s white horse, saved Frodo’s life.
Overall, Tolkien conveys that the light’s role is to show the way to triumph, not to further gloom. The dark continually assaults the good forces, but the light would always intercept to give hope. As a devout Catholic, the literary work might suggest that God is the light that is to be trusted in a life that is vulnerable to immorality—the light that reveals the path to refuge and righteousness.