And it came about, while Israel was living in that land, that Reuben went and slept with his father’s concubine Bilhah, and Israel heard about it. Genesis 35:22a (NASB)
Genesis 35 is where God changes Jacob's name to Israel. It's also where the internal structure of the nation of Israel begins to take shape, starting with the fall of Reuben.
Reuben's fall, according to the Midrash, triggers the distribution of the Portion of the Firstborn, the Kingdom, and the Priesthood:
And after Rachel’s death Jacob transferred his tent into the tent of Bilhah her maid-servant. And Reuben became jealous in behalf of Leah his mother, and he entered Bilhah’s and forcibly removed thence the bed of his father. At that time Reuben was deprived of the portion of the first-born, the kingdom, and the priesthood, for having profaned his father's bed; and the right of the first-born was given unto Joseph, and the kingdom to Judah, and the priesthood to Levi, because Reuben had profaned the bed of his father. Sefer HaYashar, Midrash on Genesis, Vayishlach 16