This section of scripture displays God's sovereignty. In chapter 20, God kept Abimelech from sinning with Sarah after Abraham passed her off as his sister. In chapter 21, God visited Sarah and caused her to conceive Isaac. In Chapter 22, God provided the sacrifice in place of Isaac.
God directs the affairs of men to accomplish his will. Daniel 4:35 says "he does according to his will among the host of heaven and amount the inhabitants of the earth and none can stay his hand or say to him "what have you done".