These are two sentences from Li Bai's The Tiger's Journey, written to the calligrapher Zhang Xu.
Because Zhang Xu served as a county captain in Changshu, the poem compared him with Xiao He and Cao Shen, ministers of the early Han Dynasty who had served as officials in Peizhong, saying that he would also have great successes in the future, "climbing the dragon and attaching himself to the phoenix". When the time comes, do something great.
The literal translation is
Xiao He and Cao Shen also once served as minor officials in Peizhong, (so you) will also have their moments of success