Why did Yue Zun write his life book?

Saved 654.38 million troops. Yue Zun used Xiaolan to repair the book of life, hoping to bring 100,000 Vietnamese troops sealed by the North Wind Sword back to life. The story of Zang Lan Jue was originally just two people meeting, knowing each other and falling in love, but I didn't know that Xiaolan was brought back to Cangyanhai by the oriental green, and Xiaolan fell in love with the overbearing oriental green in the process of getting along.