The first three times the Bible uses the word barren are in reference to the wives of Abraham, Isaac and Jacob/Israel.  To be barren means to not be able to reproduce.  Sarah, Rebecca, and Rachel we’re all barren.  The miraculous thing about all of these barren women was they were the ones chosen by YeHoVaH to produce the children of the covenant.  What is impossible for man is not impossible for YeHoVaH. Isaac was sixty years old when his twins, Esau and Jacob, were born.   The birthright is the right of the firstborn. YeHoVaH would establish the Law pertaining to the birthright later, but here it is believed that the firstborn son would inherit the family property and responsibility of the head of the house when the father dies.  Listen to the saga of how Esau came to sell his birthright to Jacob.