Our society loves rainbows. Children to adults, we love to spot them in the sky or find them in a waterfall. Although science has helped us understand why they appear, that doesn't change the beauty of them.
The key to this story is judgment and grace. God saw that the world needed judgment, that judgment could only be firm and swift. However, God saw Noah and his family were worthy of grace. Because of that grace, God spared their eight lives.
When the time came, Noah was faithful to God, showing that God's choice to show grace to Noah was a good one. When we get to the end of the story, we see Noah offering a sacrifice to God as soon as he gets off the boat. Noah chose to honor God for his faithfulness. In return, God made a covenant with Noah and the generations that followed never to bring that level of judgment upon the earth again. The sign of that covenant was the rainbow.
Wheather you believe this story is literally true, or Jewish hyperbole, the message is the same. God showed the world judgment and Noah's family grace. This is the story of the scriptures.