Sailhamer, John H. The Pentateuch As Narrative. Grand Rapids: Zondervan, 1992.
Chapter 1, “Genesis” pp. 81-240.
Part 2 “Account of Abraham (11:27-25:10) pp. 137-184. Section F “Abraham, Isaac, Ishmael, and Abimelech (21:1-34)” pp. 176-177.
In Genesis 21 Isaac is born. Sailhamer points out that the lengthy discussion of chapter 18 is completed with a rather short account, simply reinforcing God’s faithfulness to keep his promises (Sailhamer 1992, 176). “The celebration of Isaac’s coming of age was the occasion for the account of the expulsion of Ishmael” (Sailhamer 1992, 176). The contrast between the child of promise and the child Ishmael continues to develop. Finally in the chapter we are reminded that Abraham still lives with the Philistines. He has not inherited the Promised Land and Isaac is not born in the place he is to inherit (Sailhamer 1992, 177).