Though we see only a small, essential portion of what God instructed Noah about life after the Flood, this context is enough to know that He is providing a basis for the establishment of laws regulating social conduct.
Why is that necessary? The reason given is because man is in the image of God. Man is being prepared for something far exceeding that of any other part of God's creation.
Man, like God, is a being who can make choices. Unlike the rest of the physical creation, man is not a creature of instinct, reacting according to preset patterns, but one who must analyze and choose to do the right as stipulated by law.
Animals do not react by understanding and analyzing law and then making a rational decision. Yes, they react to laws, but they are reacting to ones set within their brains, instinctive patterns according to which they must react.
Man does not react instinctively. Because he has mind, he is free to do the wrong thing! But he is also free to do the right thing, as stipulated by law.
John W. Ritenbaugh
Other Forerunner Commentary entries containing Genesis 9:6: