Genesis 21 is a pivotal chapter in the book of Genesis, as it marks the birth of Isaac, the son of Abraham and Sarah. This is a significant event in the Bible, as it is the fulfillment of God's promise to Abraham that he would have a son. The chapter begins with the announcement of Sarah's pregnancy, and the joy that Abraham and Sarah experience as a result. The chapter then goes on to describe the birth of Isaac, and the celebration that follows.
The chapter also includes the expulsion of Ishmael, Abraham's son by Hagar. This is a difficult moment for Abraham, as he is forced to choose between his two sons. However, God reassures Abraham that Ishmael will be blessed, and that his descendants will be numerous.
The chapter ends with a covenant between Abraham and Abimelech, a Philistine king. This covenant serves to protect Abraham and his family, and to ensure that they will be able to live in peace in the land of Canaan.
Overall, Genesis 21 is an important chapter in the Bible, as it marks the birth of Isaac and the fulfillment of God's promise to Abraham. It also serves to demonstrate God's faithfulness to Abraham, and his willingness to protect and bless him and his family.