Tyndale Open Study NotesGenesis 21

See Genesis 18:10.

Abraham responded in faith by naming his son Isaac and circumcising him according to the terms of the covenant (see 17:9–14).

Isaac was born 25 years after God first made the promise to Abraham (compare 12:4).

Sarah was filled with joy and praise for this amazing event. Only God could enable her to have a child.

Sarah’s made a wordplay with the name Isaac (Hebrew yitskhaq, meaning “he laughs”). It shows how laughing in disbelief turned to laughing in joy when God fulfilled the promise (18:12). Isaac’s name might reflect the pleasure of God and his parents at his birth. Sarah knew everyone who heard about this would laugh and celebrate with her.

God used the incident of Ishmael’s mocking Isaac to separate Ishmael and Hagar from the family and the child of promise. They would constantly threaten the promised descendant if they remained with the family.

The feast for Isaac’s weaning probably happened when he was three. Ishmael was around 17 years old at that time (16:16). Sarah saw Ishmael mocking her son, Isaac. The verb metsakheq (“mocking”) is related to the word for “laughter.” This theme (21:6) becomes negative because of Ishmael’s mocking.

Earlier, Sarah mistreated Hagar and forced her to flee (16:6). Later, when Hagar’s son mistreated Isaac, Sarah insisted that the slave woman and her son leave.

Abraham was upset when Sarah asked him to send Hagar and Ishmael away. God told Abraham to agree, promising that Ishmael would also have a future as Abraham's descendant.

God rescued Hagar and Ishmael in the wilderness and promised them a future (compare 16:7–14). This passage is like chapter 16, but there are key differences. God saves Hagar and Ishmael, but there is no special naming. God repeats the promise to Hagar, but she is not told to return to Sarah.

These repeated themes show God's plan for Hagar and Ishmael. As Joseph later explained to Pharaoh, a repeated event confirms God's plan (41:32). God did not leave Hagar and Ishmael alone. He met them in their time of despair (compare 16:7). He gave them what they needed and promised again that Ishmael would start a great nation (21:13; see 16:11–12).

Paul uses this story in his letter to the Galatians to show that God’s people must let go of anything that could block God’s promise from being fulfilled (Galatians 4:21–31).

a bowshot away: This means the distance an arrow can travel when someone shoots a bow. The phrase connects with Ishmael’s future work as an archer (21:20).

Abimelech wanted a treaty so that Abraham would not deceive him. He knew that God was blessing Abraham, even though Abraham had not always been truthful (20:9–10). This sad contradiction made the treaty necessary.

By contrast, God’s people are called to speak truthfully. Paul teaches believers to speak the truth in love (Ephesians 4:15, 25). Jesus also warned against using oaths to distort the truth (Matthew 5:37; James 5:12).

At the high point of this passage, it explains the name of Beersheba, where Abraham lived (21:31–34). The name is linked to the covenant (a binding agreement) that Abraham made with the people of the land. This agreement allowed him to live there in peace and safety.

In this way, God’s promise was beginning to come true (12:7; 13:14–17; 15:7, 18–21; 17:8).

The theme of the well appears again (see 16:14; 21:19). God provided water, symbolizing blessing, in the dry wilderness. Later, he even brought water from a rock for Israel (Exodus 15:22–27; 17:1–7; Numbers 20:1–13).

Abraham gave gifts to Abimelec (compare 20:14). These gifts helped confirm his legal right to live peacefully in the land and to claim the well as his own. Beersheba marked another step toward the fulfillment (completion) of God’s promise.

The Philistines mentioned in Genesis are not the same as the Philistines in Judges through Kings. The earlier group had Semitic (ancient Near Eastern) names, such as Abimelech, and they followed Canaanite culture.

The later Philistines were likely from the Aegean region (near Greece). They had different customs and culture. They seem to have come to Canaan by sea around 1200 BC, during the time of the judges.

Because of this, the name Philistines in Genesis is probably used to describe the earlier people of the region in a way that later audiences would understand.

• A tamarisk tree requires a lot of water. Planting it showed Abraham felt secure in his land rights and trusted God to provide water in the desert. Although he was a foreigner, living under the tree represented peaceful security (compare Zechariah 3:10).

• there he called upon the name of the LORD: See study note on 12:8.