Genesis 25:12 - 16

"This is the account of the family line of Abraham's son Ishmael, whom Sarah's slave, Hagar the Egyptian, bore to Abraham. These are the names of the sons of Ishmael, listed in the order of their birth: Nabaioth the firstborn of Ishmael, Kedar, Adbeel, Mibsam, Mishma, Dumah, Massa, Hadad, Tema, Jetur, Naphish and Kedemah. These were the sons of Ishmael, and these are the names of the twelve tribal rulers according to their settlements and camps." NIV translation

In this family line, we see that God kept His promise to Hagar and to Abraham. In chapter 16, God had promised Hagar that He would make her descendants numerous and, in chapter 17, God promised Abraham that twelve rulers would come from Ishmael. 

Genesis 25:17 & 18

"Ishmael lived a hundred and thirty-seven years. He breathed his last and died, and he was gathered to his people. His descendants settled in the area from Havilah to Shur, near the eastern border of Egypt, as you go toward Ashur. And they lived in hostility toward all the tribes related to them." NIV translation

Ishmael's family lived in the northern part of what we call Saudi Arabia. The hostility that was predicted by God towards the sons of Isaac continues even to this day.

Genesis 25:19 & 20

"This is the account of the family line of Abraham's son Isaac. Abraham became the father of Isaac, and Isaac was forty years old when he married Rebekah daughter of Bethuel the Aramean from Paddan Aram and sister of Laban the Aramean." NIV translation

Now, we are introduced to the family of the son of the promise and are reminded of the answered prayer in finding him a suitable wife.

Genesis 25:21 & 22

"Isaac prayed to the Lord on behalf of his wife, because she was childless. The Lord answered his prayer, and his wife Rebekah became pregnant. The babies jostled each other within her, and she said, 'Why is this happening to me?' So she went to inquire of the Lord." NIV translation

Like her mother-in-law, Rebekah was barren and so Isaac prayed for her. God heard and answered the prayer by giving them twins but the twins struggled with each other even while they were still in the womb. Rebekah did not know what was going on so she took the matter to the Lord. That is a reminder to us that, if we don't understand what is going on in our lives, we can ask God because He does know the why as well as the what.