A man might have two wives and love one but not the other. Both wives might have children, and the firstborn son might belong to the wife that the man doesn’t love.
She became pregnant again and gave birth to another son. She said, “Certainly, the Lord has heard that I’m unloved, and he also has given me this son.” So she named him Simeon [Hearing].
When the day comes for the father to give his sons their inheritance, he can’t treat the son of the wife he loves as if that son were the firstborn. This would show a total disregard for the real firstborn (the son of the wife he doesn’t love).