What does Confucius mean by taking his brother's son as his wife?

Bai Gui (1), south banyan three blessings Confucius married his brother's son.

Nan Rong put "the temple of Bai Gui, which can be grinded;" After reading several poems, Confucius married his niece.

(1) Bai Gui-Bai Gui's four poems are all in the Book of Songs, which shows that Bai Gui's stain can be worn away; There is no way to remove the stain from our words. Probably Nan Rong is a cautious person, so he can do "the country has a proper way, not in vain;" There is no way for a country to escape punishment. "