Claim. Children complete their parents by uniting the parents’ two lineages into one, so filial piety is not just gratitude — it is the mechanism by which the parents themselves are perfected.
Elaboration. SMM asks what parents hope for and answers: “There is no unified root of the lineage with just a mother and a father. They need to have children in order for the lineage to continue. When sons and daughters love their parents, then the unconnected lineages of the parents become unified through the child” (CSG 14.1 §1, 223-174, 1991.11.10). “The father and mother become perfect through sons and daughters practicing filial piety.” The child is described as the nucleus through which the parents’ life, love, and lineage become substantial: “We represent our parents’ life, love and lineage… your love, life, and lineage have become its embodiment.” Filial piety thus closes the four-position-foundation loop — parents are not whole until the child completes them, and the child’s perfection comes back through their own marriage.
See also. csg-perfecting-the-trinity-grounds-filial-piety-tribally