《左传·僖公·僖公二十四年》
当它笼络天下的时候，尚且害怕有外界的侵犯；抵御外界侵犯的措施，没有比亲近亲属再好的了，所以用亲属作为周室的屏障。
其怀柔天下也，犹惧有外侮，扞御侮者莫如亲亲，故以亲屏周。
When it unified the world, it still feared invasion from the outside, there is nothing better than being close to relatives as a measure against invasion from the outside, hence it used relatives as a shield for Zhou.