Cash is the oldest son. He is the one whom Addie refers to when she says that she robbed Anse of one son. Cash was born at a time when his mother had just discovered that words are meaningless and that only through acts can people achieve an awareness of life. Thus, Cash seldom speaks in the novel and usually only after some action is performed. Furthermore, he seems to be concerned with only one act at a time. Thus, he is the natural choice for the building of the coffin because he, like Addie, knows that the finished product is more important than the words expressed about it. And as he builds, he does not seem to be aware that his mother is actually dying — all his energies are concentrated upon the building of the coffin. His first section comes after he has the coffin almost completed, and this section simply enumerates the thirteen steps or reasons why and how he built the coffin.
Like Addie, Cash seems to know that words are useless. And when he breaks his leg a second time, he tries to protest that he doesn't want the cement on his leg, but again the words are useless and he simply resigns himself to the torture. He does not even bother to formulate words enough to express his tremendous suffering.
When Darl is sent off to the insane asylum, Cash seems to be somewhat justified in his view toward words. He says, "ain't none of us pure crazy and ain't none of us pure sane until the balance of us talks him that-a-way." The act itself that Darl performed seems to Cash to be right; therefore, it was the talking about the act that convinced people that Darl was insane.
Cash reflects Addie's views about the uselessness of words and sees only one action at a time, and his main concern is with each immediate action.