Why did the Emperor of Heaven announce Xi to the emperor?

Test his son Xi Xuan to see if he can inherit his mantle. Xi Xuan is God's favorite son, but this child is kind in nature and fearless of people and things, so he is doomed to suffer.

Xihuan, also known as Sifeng, is the third son of the Emperor of Heaven and Earth. Sifeng is the son of the Emperor of Heaven. Thousands of years ago, his name was Xihuan. In order to protect the God of War, he was beaten to pieces by Bailing Emperor. After that, the Emperor of Heaven did not shelter him, but let him enter reincarnation with the God of War.