Genesis 4:6-7, provides words of encouragement to Humanity. We make mistakes. We get angry because of our mistakes. This section provides Humanity the means of getting out of the rut. It is called IMPROVEMENT. If we work on overcoming our mistakes, it will be appreciated. If we cannot get out of this rut, we can take ourselves into a downward spiral of despair. In sum, we all need to practice “self improvement.” It, however, requires working on it.
As noted in the famous passage from Genesis:
And the Lord said to Cain, “Why are you annoyed, and why has your countenance fallen?
Is it not so that if you improve, it will be forgiven you? If you do not improve, however, at the entrance, sin is lying, and to you is its longing, but you can rule over it.”
The sad ending to this particular story was the Cain went out and killed his brother Abel. At that point in Bible History, the Ten Commandments had yet to be provided to Humanity.
The Ten Commandments Project 