Scripture: Genesis 6:6-7
The Lord regretted that he had made human beings on the earth, and his heart was deeply troubled. 7 So the Lord said, “I will wipe from the face of the earth the human race I have created—and with them the animals, the birds and the creatures that move along the ground—for I regret that I have made them.”
In Genesis 6:7, God says that He's going to wipe the human race from the earth because of their sinfulness. Then, He adds that He's going to destroy all the animals along with them.
Why would God do this? Why are the animals being punished for humanity's sins? That doesn't sound fair!
But we have to remember that in Genesis 1:28, God made humans the rulers over the animals. And as the saying goes, everything rises and falls on leadership.
In Genesis 1:29-30, God gave humans and animals permission to eat only plants. Everything was peaceful. It was "very good." But after Adam and Eve sinned, creation fell with them. Rather than remaining at peace with one another, the animals began hunting one another and fighting for territory. The sin of our first parents had consequences for the whole created order. Even the ground was changed because of their sin (Genesis 3:17-18).
Our sins carry consequences as well, and never for us alone. Adam and Eve's sins had consequences for the animals and the ground. The sins of the people of Noah's day threatened to destroy every living thing. And our sins affect everyone around us.
Think of the last time you sinned, or fell short, of God's standard. What were the consequences? I'm sure there was some effect on you, but did someone besides yourself become upset? Were someone's feelings hurt? If not - maybe if no one knew what you did and so no one else seemed to be affected - think about the good you could have been doing for someone instead of doing... whatever it was you were doing. Or think about the attitude that your sin gave you afterward that colored how you interacted with the next person you saw.
It's not always easy to see, but sin never affects just the person committing the deed. The sin is either committed against someone else directly or it indirectly affects them through the loss of a benefit you otherwise could have provided.
At its core, sin is selfishness because it grants your (momentary, fleeting) desires above the good of others. The sins of the people of Noah's day didn't hurt only them, and our sins don't hurt only us.