Chapter 6 of Genesis says that as the population of people grew in numbers that God saw that they were wicked and that every thought they had was evil; therefore, he decided to destroy all of them except the one who was a good man: Noah.
God spoke to Noah because he knew God and worshipped him faithfully to build the ark. In chapter 6 of Genesis, the specific instructions for the ark are stated by God who said:
One cubit is 18 inches today. (When you do the math, the Ark was very small so there must have been something different back in Noah's time.)
Make your self of gopher wood with rooms and cover it inside and out with pitch. It will be built 300 cubits long 50 cubits wide and 30 cubits high. Make a window for the ark and finish it to a cubit from the top. Set the door of the ark in the side. Make it with lower, second and third decks.
Because God found not one righteous man in the world except Noah.God instructed Noah to build this ark and how to build it,which took 125 years.People persecuted Noah for doing this and ridiculed him.Noah remained faithful to God and continued.God at this point was sorry he ever created man because evil was widespread as it is now.When the ark was built,Noah was able to save his family and their children,and two of everykind of living thing.By faith,Noah waited in the ark 7 days and God sealed the door and the rains came,some people beat on the door yelling please-let me in!! But they didn't believe God was going to destroy mankind until it was too late,and their reasons were for safety-not love of God.And so the rains kept and the floods roared to 25 feet above the highest mountain peaks and all mankind was killed in the floods.God promised to never destroy the earth in this manner again-he knew the hurt of it and knew the pain,But nobody loved the Lord except Noah.
He flooded the earth because he saw how the people in Israel (when everyone lived at this time lived) and flooded the earth. Everyone died except Noah, his wife, Noah's 3 sons, and all there wives. Also some birds an animals lived. In the bible it says that a rainbow is god's promise to never flood the earth again.
The book of Genesis was written a long time ago. Since then we have discovered fossils of fish and shells on top of mountains. Scientists will say that these mountains rose up from the sea. You can decide for yourself.
It happened because the Bible says it happened. The Bible is really the only veritable key to the past! It is more likely for heaven and earth to be destroyed than for the Holy Scriptures of God to be wrong (Matthew 24:35 Heaven and earth shall pass away, but my words shall not pass away .KJV).
The unbelievers do not have the Holy Spirit of God dwelling in them and are prone to mistakes for the simple reason that they don't approach the Bible with a sincere hearth in search for truth.
I will enumerate some of the mistakes these people make in assuming the World Wide Flood was a legend.
#1 - They assume that based on the dimensions of the ark mentioned in the Bible, that it was too small for all the animals on board. Well, the measurements were given in cubits. It is possible that Noah was taller than average man today, thus making his "cubit" longer. It's mentioned in Gen. 6:4 that "there were giants in the earth in those days..." It's possible that Noah and the average height of people was taller than what it is today.
#2 - They ignore the species problem, and think that the species today were back then too. That is not true. 4400 years ago there weren't all the varieties of dogs, horses, roses, etc. Therefore, I believe he brought on board examples of the same "kind" not species. And the kinds are far less than the total number of species.
#3 - The Bible clearly states that the animals that were supposed to be preserved on board were the ones in which there was "the breath of life" (Gen. 7:15). And in Gen. 7:22 says that "All in whose nostrils was the breath of life, of all that was in the dry land, died." So one can clearly see that Noah didn't have to bring on board insects, fish, marine mammals, crustaceans, etc. He only preserved the life of land mammals and birds, which do have the breath of life in their nostrils.
#4 - Skeptics assume all the animals on board were adults. Anybody that is 600 years old like Noah was when the Flood came, knew that you don't need to bring in the biggest ones you can find. He could have brought in babies which are smaller, weigh less, eat less, and sleep longer.
#4 - They assume all the water of the Flood came from rain when in fact, the Bible clearly teaches in Gen. 7:11 "...the same day were all the fountains of the great deep broken up, and the windows of heaven were opened." Most of the water came from under ground chambers and not from rain like ignorant skeptics believe.
#5 - They assume all the high mountains were as high as they are today. The elevation of the mountain chains follows in parallel with the oceans shore line. Plus the seashells that were found petrified even on top of Mt. Everest is a clear proof that that mountain was once under the water.
Because it was fated and becuse god told him to