Genesis 8:21-22 New International Version (NIV)

21 The Lord smelled the pleasing aroma and said in his heart: “Never again will I curse the ground because of humans, even though every inclination of the human heart is evil from childhood. And never again will I destroy all living creatures, as I have done.

22 “As long as the earth endures,
seedtime and harvest,
cold and heat,
summer and winter,
day and night
will never cease.”

Many, many times throughout the Bible, God shows his love and patience toward us in order to save us. He realizes that our hearts are evil, but he will continue to reach out to us. When we sin and fall away from God, we deserve to be destroyed by his judgement, but God promises to never destroy the earth until the judgment day when Christ returns to destroy evil forever. Every year and change of the season is a reminder of this promise.