The Birth of Shet (Seth)
130 years after the creation Shet is born to Adam — «for God has granted me other offspring in place of Abel». All humanity descends from him.
After Abel's murder and Cain's exile, the human line hangs by a thread: one son dead, the other a banished killer. The Torah dates it exactly: «Adam lived 130 years and fathered a son in his likeness, after his image, and called him Shet». Chava explains the name: «God has granted me other offspring in place of Abel, whom Cain killed» — the first name in the Torah given as a statement of hope.
Shet anchors the entire genealogy: Genesis 5 runs Adam — Shet — Enosh and on to Noach, and from Noach to all post-flood humanity. Cain's line, listed in chapter 4 with its smiths, herdsmen and musicians, ends at the Flood. By the Torah's reckoning every living person descends from Shet. The year 130 is also the hinge of the chronology: every later date, down to the Flood in 1656, is built on the chain of «he lived so many years and fathered» in chapter 5.