How does this book explore the idea of duty over love?

In As I Lay Dying, duty seems to be more of a factor and motive than love. The Bundrens are basically taking Addie’s body to Jefferson to bury because of familial duty. Cash does his duty in making Addie’s coffin. Darl and Jewel do their duty in running an errand for Tull for three dollars. The Bundrens are poor, so this three dollar job seems to be more important than being there when their mother dies. The family is tied together by obligation, rather than any emotional tie.