Isaac was the promised child born to Abraham and Sarah in their old age, fulfilling God's promise to make Abraham's descendants into a great nation. God had promised Abraham that all families of the earth would be blessed through him, even though Abraham and Sarah were unable to have children at the time. Later, when Abraham was 99, God promised again to multiply his descendants greatly. Their son Isaac was conceived and born miraculously to 90-year-old Sarah, just as God had promised, despite their old age. Sarah named him Isaac, meaning "laughter", to commemorate God making her laugh with joy at his birth.