If I become a saint, the immortal official will call me to raise horses

When Gu An, a servant, was young, he accidentally broke a jar of spiritual flowers. When he was panicked, he found that he had taken away twelve years of life!
A road to immortality was laid out in front of Gu An!
In order to cultivate immortality safely, Gu An chose to become a chores disciple of Taixuan Sect, planting herbs every day to take away the life of herbs for cultivation.
Through the evolution of life, his basic skills continued to evolve, and he deduced from the basic method to the supernatural power!
The eras changed, the stars moved, and the world changed.
The legend of immortals gradually appeared in the world.
Gu An, known as the immortal, spent half of his life to help his cultivation surpass the limit of the immortal way, achieve the realm of the saint, and surpass the heavenly way.
However, one day, an old man in white clothes with an immortal style came to visit Gu An.
"I am the Xuanqing Star Lord in the sky. Emperor Taihao heard that you have done many good deeds in the world and saved many sentient beings. You have great merits. I was sent to the lower world to summon you to join the immortal class and take up the position of the Divine Horse Heavenly Official."
"May I ask what the position of the Divine Horse Heavenly Official is?"
"There are divine horses in the heavens that can cross the sky and earth and escape into yin and yang. The Divine Horse Heavenly Official is responsible for taking care of and feeding these divine horses."
Hmm? Raising horses?