God asked Noah to build an ark, because he is going to bring his
judgement upon the world through a flood. and since Noah and his
family is the only Godly people in the world, God decided to save
them.
in other cases, God also brought calamity on people who were
terribly sinful, like the story of Sodom and Gormora (cant spell
it). God sent fire from heaven and destroyed the two cities that
were indulging in homosexual activities.
in Noah's time, there is no such thing as incest. incest is a
relatively mordern concept.
