The story of Noah and the flood was an issue of ethics and sanctions. Man lost good ethics and God imposed sanctions according to the infractions of men.
God was angered by the attachment of man to sin. God is all good, and sin, being an act of evil, drives man away from God. As a christian, I believe that God is the Creator and is sovereign over all things.
It is fairly simple in context, men had bad ethics, and therefore were inflicted with appropriate sanctions. Men have free will, and at the time of Noah, man chose to stray away from what is purely good (disobedience towards God). They received sanctions according to their ethical decisions. The negative sanction was a flood that would demolish man and beast from the earth.
Noah, however, found favor with God, therefore God chose not to inflict these negative sanctions on Noah. The favor God found with Noah, extended to Noah’s family. This gives an example of the foundational culture of a household. Noah’s obedience to God was possibly shared by Noah’s wife and sons, however, there is no account on this. It is possible that because God found favor in Noah’s obedience, that the descendants of Noah, would also be pure, and would re-populate the earth. It is also possible that if Noah was a good man, that God chose to not take Noah’s family. There is not direct account on this, and interpretation is not accurate when the proper details are not included in the original account.
God gave grace to Noah, and instructed him to build an ark. He also instructed Noah in bringing animals onto the ark. When the time for the event of the flood had come, it rained for 40 days and 40 nights, and the flood swept man and beast from the face of the earth leaving alive only the menn and beasts that dwelt in the ark.
God signaled to Noah through a dove that the waters had withdrawn from the land, and again, God told man to be fruitful and multiply.
After the flood, God made a covenant with man. A covenant is an agreement that brings about a relationship between God and his people. In this covenant, God promised that never again would he repeat the event of the flood. It is the common belief, that God symbolized this covenant with the rainbow. Men continued to sin, but this would be settled in a different kind of judgment. There are different beliefs of the judgment between God and man, but God made a covenant with man that this judgment would never again be the destruction of all mankind.
There were many covenants to follow this one, but this one is considered foundational. Even among atheists who do not believe in the sovereign God behind this series of events, most of them are familiar with the idea of this covenant. The story of Noah and the flood, and the covenant is basic to western literature.