“It rains continuously and you don’t know the end of summer, but you only know the depth of autumn after a dream” means: It describes that time passes very quickly. In the change of time between sunny and rainy days, summer has passed and autumn has come.
From Fan Chengda's "Xi Qing" in the Song Dynasty: "The plum blossoms are ripe and falling between the windows, and the bamboo shoots are growing in the forest under the wall. It rains continuously and you don't know the end of spring, but you can feel the depth of summer when it clears up."
Translation:
The plums between the windows fell when they were ripe, and the bamboo shoots under the wall grew into a bamboo forest. It rains continuously, and when it clears up, I don’t even know that spring has passed and summer is already very late.
"Xi Qing" is a six-character quatrain created by Fan Chengda, a poet in the Song Dynasty. Fan Chengda likes to plant plum trees in front of the window so that he can taste green plums in summer and enjoy plum blossoms in winter. Fan Chengda (1126-1193), also known as Zhi Neng, was known as Shihu layman. Han nationality, from Wuxian County, Pingjiang (now Suzhou, Jiangsu Province). Poet of the Southern Song Dynasty. Posthumous title Wenmu. Starting from the Jiangxi School, he later studied the poetry of the Middle and Late Tang Dynasties, inherited the realism spirit of the New Yuefu poets such as Bai Juyi, Wang Jian, and Zhang Ji, and finally became his own school. The style is simple, fresh and charming. Poetry has a wide range of themes, and the works that reflect the content of rural social life have the highest achievements.