It is a good rainy season when spring comes. There are several reasons for using personification rhetoric.

"Good rain knows the season, when spring comes." Good rain knows the solar terms of rain, just when plants sprout and grow. It rains in time.

Reason: Rain has no perception and consciousness, and it doesn't know the season. Here, rain is endowed with the perception and consciousness of knowing the seasons, just like knowing the solar terms. When plants grow most vigorously in spring, rain comes. So this sentence is personified rhetoric.

I hope you can understand this!