The characters combine powerfully. 列祖 (liè zǔ) means “all the generations of grandfathers/paternal forefathers,” and 列宗 (liè zōng) means “all the generations of the clan/lineage.” Together, 列祖列宗 (liè zǔ liè zōng) creates a comprehensive and solemn phrase that leaves no one out—it is the entire, collective body of your ancestors.
The term 列祖列宗 is deeply rooted in Confucian values, especially 孝 (xiào), or filial piety. In traditional Chinese culture, an individual is not seen as an isolated entity but as a single link in a long, continuous family chain. Your existence is a gift from your parents, who received it from their parents, and so on, all the way back to the beginning. This creates a profound sense of responsibility. Your actions, both good and bad, reflect not just on you but on your entire family, living and dead. The ultimate goal is to 光宗耀祖 (guāng zōng yào zǔ)—to bring glory and honor to your ancestors. Conversely, the ultimate shame is to do something that would make you unable to “face your ancestors” (没脸见列祖列宗).
This is a formal and often serious term. You won't hear it used in casual, everyday conversation about the weather.