According to Gen 6:3 the Lord said, "My Spirit shall not strive with man forever, because he also is flesh; nevertheless his days shall be one hundred and twenty years." Before the flood, God gave men a hundred and twenty years to repent of their sinfulness, but they ignored Him. They did not realize that God meant what he said, they watched as the one righteous man and his family prepared for the destruction, they probably laughed at him. But Noah listened to God and did as He was instructed, and he and his family was saved. The door was opened and Noah and his family went in, and then it was closed.