What is the meaning of "the moon comes first near the water tower, and flowers and trees turn to spring in the sun"

This allusion comes from Ye Qingliu written by Yu Wenbao in the Southern Song Dynasty. Fan Zhongyan was a politician and writer in the Northern Song Dynasty. When he was a magistrate in Hangzhou, he recommended some subordinates to be officials. There was a man named Su Lin who was ordered to patrol outside at that time and was not noticed by Fan Zhongyan. Su Lin wrote a poem for him. There are two lines in the poem: "the moon comes first near the water tower, and flowers and trees are easy to spring in the sun." On the surface, it is a natural phenomenon, but the actual moral is: everyone around you got promoted first, but I didn't get reused. Fan Zhongyan understood his feelings and wrote a letter of recommendation for him. Later, Surin was also promoted.