Because Reuben defiled his father's bed by sleeping with Bilhah, his concubine:
Genesis 49:3-4New King James Version (NKJV)3 "Reuben, you are my firstborn,
My might and the beginning of my strength,
The excellency of dignity and the excellency of power.
4 Unstable as water, you shall not excel,
Because you went up to your father's bed;
Then you defiled it-
He went up to my couch.
Reuben was the firstborn son of Jacob (Genesis ch.29) and ancestor of the Israelite tribe that bears his name. He played a part in the saving of his half-brother Joseph (see Genesis ch.37). The inheritance of the tribe of Reuben was in the Transjordan (Numbers ch.32).
The Reubenites are the descendants of Jacob's [Israel's] firstborn son, Reuben."These are the sons of Israel; Reuben, Simeon, Levi, and Judah, Issachar..." (I Chron.2:1).
Jacob Reuben was born in 1931.
Reuben was the eldest son of Jacob and Leah. He lost his birthright to Joseph(The first born son of Jacob and Rachel) and it was Joseph who received the blessing from Jacob, which should have gone to Reuben. Reuben became an enemy of Joseph for many years but finally made up. The tribe of Reuben became of less importance politically, and its members became less as the years went by.
In the Bible, Ruben was not specifically mentioned as being related to Saul. Rather, Ruben was one of the twelve sons of Jacob and the ancestor of the tribe of Reuben. Saul was from the tribe of Benjamin.
The oldest son of Jacob and Leah was Reuben. He was the firstborn son and the founder of one of the twelve tribes of Israel.
While Jacob was mourning Rachel, Reuben slept with Jacob's concubine Bilhah.
The tribe of Reuvain settled in the Transjordan.
Reuben = ראובן (pronounced reh-oo-ven)
the eye tribe
Jacob is a part of the Quilets tribe.
The 12 tribes of Israel were descended from the 12 sons of Jacob (see the Book of Genesis in the Bible). When the Israelites entered the land of Canaan, each tribe was allotted part of the country, and Reuben was allotted the land just east of the Dead Sea.