Genesis 34

Here we get the beginning of an explanation as to why Judah is blessed above his brothers.  Keep in mind that as Leah's fourth son, he wasn't entitled to much.

The second and third sons killed an entire city. Admittedly, Shechem was probably not even a small town by our standards, and the killing was done to avenge the rape of their sister, Dinah. Still, Simeon and Levi lied, and their bloodlust should have been with the one who defiled her, not with his whole town.

So why wasn't the first son, Reuben, chosen? Patience ...