Abraham marries Keturah and has six more sons. We don鈥檛 know if that was before or after the death of Sarah. Abraham鈥檚 death is listed, but this event isn鈥檛 written down in order that it happened. According to Genesis 21:5, Abraham was 100 when Isaac was born. According to verse 26, Isaac was 60, when his sons were born, so Abraham was 160 when his grandsons were born and 175 when he died. Moses tells the story in a way that closes out the life of Abraham before moving on to the life of Isaac鈥檚 sons. Ishmael鈥檚 offspring are also listed in this chapter, showing God keeping his promise to Abraham from Genesis 17:20; which is another way of closing out the life of Abraham. Since Isaac was 40 when he married and 60 when his sons were born, Rebekah and Isaac had to wait 20 years for her to become pregnant.
What is clear from this chapter is that God keeps his promises. His promise to Abraham was that he would be the father of many nations. This happened through Isaac, Ismael, and his other sons. He promised that Isaac would be the father of a nation. Although it took a while, Abraham saw his grandsons live to age 15. We have many promises from God as well: our sins are forgiven, we have the Holy Spirit inside us and we have the power to overcome sin in our lives. Like Abraham, we can depend on God鈥檚 promises, even when it doesn鈥檛 look or feel like it.