Text 39

kula-ksaye pranasyanti
kula-dharmah sanatanah
dharme naste kulam krtsnam
adharmo ’bhibhavaty uta

Translation

With the destruction of dynasty, the eternal family tradition is vanquished, and thus the rest of the family becomes involved in irreligion. 

Commentary by Srila Prabhupada 

In the system of the varnashrama institution there are many principles of religious traditions to help members of the family grow properly and attain spiritual values. The elder members are responsible for such purifying processes in the family, beginning from birth to death. But on the death of the elder members, such family traditions of purification may stop, and the remaining younger family members may develop irreligious habits and thereby lose their chance for spiritual salvation. Therefore, for no purpose should the elder members of the family be slain.

Commentary by Sri Visvanatha Cakravarti Thakur

The right conduct maintained by the family which has passed down from many generations (sanatanah kula dharmah) will be destroyed with the destruction of the family (kula ksaye).