The Seasons

"Such a man (a Real Man) is unaffected by circumstances, his demeanour is full of repose, his (facial) expression undemonstrative. His coolness is that of autumn, his warmth that of spring. His emotions follow their natural course like the round of the four seasons. His harmony with natural things is beyond all human estimate..."(Blyth, 43-4)
This is part of a teaching about conduct. Even in this early time, people felt very connected to the world around them. They also felt indebted to nature, who provides their life force and human form.
"A child must go obediently East, West, South, North, according as his parents tell him. In and Yo (Ying and Yang) are not merely a man's mother and father. When they bring me close to death, and I oppose them, I am rebellious and unruly; they are blameless. Great Nature, by bestowing upon me (human) form gives me my place (in the world); by life, enables me to work; by old age, contentment; by death, cessation of existence."(Blyth, 45)
Confusianism also speaks of nature in this sort of personification. Confusius considered nature to be 'the Way.' This means that nature was seen as the way of life, the controlling force in everyone's existence.
"The song of the birds, the voice of insects, are all means of conveying truth to the mind; in flowers and grasses we see the messages of the Way. The scholar, pure and clear of mind, serene and open of heart, should find in everything what nourishes him."(Blyth, 76)
While these ideas spread to Japan, they were probably welcomed because the Japanese culture had already established similar views.
"Kami thus refers to the essence of many phenomena that the Japanese believed were endowed with an aura of divinity. Rocks, rivers, animals, trees, places, and even people can be said to possess the nature of kami."(Picken, xxii)
This kind of thought is called "animism," or the belief in indwelling spirits. Shinto also practices "animatism," or nature worship. Nature is, in this case, personified into kami. (Blyth, 150)
"To the Japanese mind, there does not exist that tremendous gulf between us and God on one hand, and animals, trees, and stones on the other. It is said with some truth that they have a feeble grasp of personality, and haiku shows a democracy among its subjects which derives from this."(Blyth, 150)
By worshipping kami, the Japanese bring themselves closer in spirit to nature, allowing them to understand its importance. It is this connection that reveals itself in waka, and creates the importance of the kigo.
"...we go back to the old savage animism, and superstition, and common life of man and spirits and trees and stones... Things have taken on something of the tenuous nature of the abstractions they turned into. Again, spring and autumn, for example, non-existant, arbitrary distinctions, have attained a body and palpability they never had before."(Blyth, 5)