The Hebrew Bible says God told Noah to enter the ark, and that rain would begin in seven days (Genesis 7:4). It does not explain why seven days. The Targum Jonathan does, and the explanation transforms the entire Flood story from divine wrath into a last-ditch act of mercy.
"Behold, I give you space of seven days," God says in the Targum. "If they will be converted, it shall be forgiven them; but if they will not be converted, after a time of days yet seven, I will cause rain to come down." This is not in the Hebrew at all. The translators invented a final ultimatum—seven days of open repentance where the entire Flood could have been called off. Humanity failed the test.
The Targum also explains what happened during those seven days. It was a mourning period for Methuselah, who had just died: "at the time of seven days after the conclusion of the mourning for Methushelach, the Lord beheld, and, lo, the sons of men had not turned." The oldest man in the Bible served as humanity's last shield. While people mourned him, God waited. When the mourning ended and nobody repented, the waters came.
And they came hot. The Hebrew says rain fell for forty days. The Targum says "the waters of the deluge came down hotly from the heavens." This detail appears in rabbinic tradition elsewhere—the idea that the Flood was boiling water, a punishment that matched the sin, since the generation of the Flood had "heated" themselves with sexual immorality.
The Targum names the month as Marchesvan, then pauses to explain that months were previously counted from Tishri, "which was the beginning of the year at the completion of the world." This footnote inside scripture reveals translators wrestling with competing Jewish calendars. Meanwhile, the giants—the Nephilim—"gathered there together with their sons and perturbed" the fountains of the deep, as if they tried to physically fight the Flood. And when the ark's door closed, it was not Noah who shut it. "The Word of the Lord covered over the door of the ark." God Himself, through His Memra, sealed it shut.