Isaac was the son of Abraham and Sarah, born when Sarah was supposedly beyond the age of childbearing. God had promised Abraham that his descendants would inherit the land of Canaan and be a blessing to all the world, yet Abraham had no son. Seeing that she was barren, his wife had him beget a son for her on her slavegirl (a legitimate practice of that time); that boy was Ishmael. However, God had determined to bring his promise about by means which were humanly impossible, so as to demonstrate that he was in full control. Isaac was born to Sarah when Abraham was 100 years old, and Ishmael was about 14.