The Decree of the Flood and the 120 Years' Reprieve
«His days shall be a hundred and twenty years» — sentence is passed, but execution is deferred for 120 years to give the generation time to turn back.
The Torah states the decree twice. First in chapter 6: «My spirit shall not abide in man forever, for he is flesh; his days shall be a hundred and twenty years.» Then plainly: «The end of all flesh has come before Me, for the earth is filled with violence because of them — behold, I am destroying them with the earth.»
The tradition reads «a hundred and twenty years» not as a new limit on human life — Noach lived 350 years after the Flood — but as a period of grace. Sentence was passed and its execution deferred: 120 years from 1536 to the Flood in 1656. The purpose was repentance. Noach was told to build the ark in plain view precisely so that people would ask what he was doing and hear the answer.
Which raises an uncomfortable question: if warning was given, why was no one saved? The sages' answer is unflattering. The 120 years passed and nobody changed. People watched the building, heard the explanation, and laughed. The reprieve failed not because it was short, but because a warning can be heard for decades and change nothing.