A great spirit child of Heavenly Father known as the archangel Gabriel was born into mortal life and given the name Noah. When he was 10 years old, he was ordained to the priesthood by his grandfather Methuselah. He is likely to have lived somewhere on the North American continent.
Noah had three sons and some daughters. While he and his sons obeyed Heavenly Father's commandments and were righteous, most of the people on Earth were wicked. The lifestyles and wicked deeds of the people in Noah's day were the same as those of people today.
Noah was not some mythical figure of legend; he was a real historical figure, and Jesus literally walked and talked with him. Jesus was very sad that the people of Earth were wicked, and he wanted to do all he could to prevent their destruction by flood. So he told Noah—one of his greatest preachers of righteousness— to tell the people to repent.
For 120 years, Noah preached repentance and baptism, trying to save the world from the Flood. But the wicked people would not listen to Noah. Rather than repent, they tried to kill Noah. There were giants on the earth in those days, and they tried to kill Noah, but the power of Jesus was with Noah.
One of the causes of the Flood was that Noah's daughters disobeyed the teachings of Jesus by marrying men who were not members of the Church. Their choice to marry unrighteous men went against Jesus's commandment, and this offense angered Jesus. Likewise, in our day there are foolish daughters who marry outside the Church, contrary to the will of God.
After giving them more than adequate time to repent, Jesus told Noah that all the wicked people and most of the animals on Earth would die. He told Noah to build a big ship and to bring aboard his wife, his sons and their wives, and two of every kind of animal. Noah was chosen to be the man to begin repopulating the earth after the Flood.
When the Flood came, all those outside Noah's ship were buried in a watery grave. Was the killing of so many people a just act? Yes, it was. So many of Heavenly Father's spirit children were waiting their turn to be born into a mortal life, and it would not have been fair to let them become the children of these wicked people who passed their wickedness on to their children. It was also merciful to these people, for it prevented them from being responsible for yet more wickedness of their own doing as well as the wickedness of their children.
The spirits of all those killed in the Flood then went to Hell where they suffered endless torture for at least the next 2,400 years. And this is the fate of all who reject the gospel, whether in ancient times or today. Many people think the story of the Flood is fiction, but it is reality, and the destruction of the wicked with water in those days anticipates the destruction of the wicked by fire at the Second Coming of Jesus.