This painting is a reference to the 5th commandment: Honor your father and mother (Ex 20:12). Depicted here is the strong, hardy, and enduring dominance of a male head of household who is juxtaposed with the seemingly fragile and powerless granddaughter. In reality, her sweet strength trumps his.
The title “Filial piety” is unusual and not a typical reference to this Christian and Jewish commandment. The commandment to care honor one’s parents is widespread in ethics around the world. It is a Confucian term 孝 and is symbolized by two figures (pictographs) that merge into one: “son” + “old” (with “old” atop “son”)—i.e. the son carries and protects his elders.