Why did Saint Zhang hit Xu Fengnian?

Saint Zhang fought with Xu Fengnian because he wanted to test whether Xu Fengnian had the ability to succeed him in guarding the world. In addition, he also wants to know Xu Fengnian's strength, and his attitude and views on the world and the world.

In the novel "Knife in the Snow", the sage of the Zhang family is a very mysterious existence. He guarded the world for 800 years, guarding against the gods in the sky. When Xu Fengnian tried to push Zhang Fuyang away, Zhang Fuyang had a big fight with Xu Fengnian. In this battle, Xu Fengnian showed great strength, which made Zhang Shengxian speak highly of him.

Generally speaking, the battle between Zhang Shengren and Xu Fengnian was to examine whether the latter had the ability to protect the world, and also to understand Xu Fengnian's strength and attitude.