Genesis 17

1 Thirteen years after Ishmael is born, God speaks with Abraham again. The name used here, "El Shaddai," refers to God's overwhelming powerfulness.
2 God would fulfill His promise to Abraham. How it would work out would depend on the relationships that he and his descendants would have with God.

God's promise of a large family was considered a great blessing in those days.

3 Abraham's immediate response is to fall down and worship God.
4 Abraham's descendants would become the Arabs and Israelites. Each of these groups broke into different nations at various points in their histories. Again, it was a great blessing to know that one would father one or more nations.
5 "Abram" means, "exalted father," and "Abraham" means, "father of many." Abraham has been used exclusively in this commentary to avoid confusion.

God often changes someone's name when He calls him into service. Names were often given to describe the person or a significant event that happened during their lifetime.

6 Ancestors were typically thought of a being "greater" than their descendants. Thus, to be the father of kings gave Abraham special honor.
7 God's promise includes Abraham and all his descendants. God's promise to bless the world through Abraham and the extension of that promise to David was fulfilled in Jesus (2 Sam 7:16). The possession of the Promised Land hinges more on the people's obedience to God. However, God has always restored Israel to their land.
10 Circumcision was to be the sign that Abraham and his descendents acknowledged and lived by the promise of God. Circumcision was not unique to Abraham's descendants, but most people in the area did not and would not practice it.
11 Circumcision literally cut away flesh. Symbolically, it represented the cutting away of fleshly (i.e., sinful) desires and focusing on God.

Circumcision refers only to males in the Bible. Female circumcision is never mentioned. Modern doctors debate about the merits of male circumcision, but overall it appears harmless and may have some benefits. Most agree, however, that female circumcision is dangerous and has a very negative affect on her sexual experience.

This "sign" was intended to be between God and the man. However, due to the general lack of privacy others would eventually find out if a man were circumcised or not.

12 This sign was to be carried out on all the males in the household. Children and servants would not have a choice in the matter. The head of the household would be responsible for giving them this sign, and then teaching them about the promise and the responsibilities it carried. Ultimately, the choice to follow God rests with the individual, but the sign would always remind them of what they were intended to be.
14 If a parent refused to circumcise his child, and the child refused circumcision, that child was to be excommunicated. The refusal of circumcision was obvious and deliberate disobedience to God.
15 "Sarai" means "my princess," while "Sarah" simply means "princess." The change is subtle, but perhaps more accurately reflects the idea that her descendants would be kings.
16 God now makes it clear that Sarah is to give birth to her own who would inherit God's promise to Abraham.
17 This question does not indicate a lack of faith, but of wonder. Abraham is so overjoyed at the "impossible" prospect of him and Sarah having a son in their old age that he laughs aloud.
18 Abraham immediately recognizes the implications for his son, Ishmael. Sarah had claimed Hagar's child as her own, but would likely reject him after having her true son. Abraham had probably been raising Ishmael as if he were the Promised Child, but now Ishmael's life expectations would be shattered. Abraham asks that God would bless Ishmael.
19 God is very clear that Isaac, Abraham's yet unborn son, would inherit the Promise.
20 Although Ishmael would not receive the Promise, he would still be blessed. This is in accordance with the promise to Hagar (Gen 16:10).
21 There was a time span of approximately 26 years between the Promise (Gen 12:2) and the birth of Isaac, which began the fulfillment of the Promise. God fulfills His promises in His own time. Only God knows the best timing for these things, so we must be patient. Abraham and Sarah tried to rush God's promise and fulfill it on their own. The result was heartache and seemingly permanent enmity between the descendents of the two half-brothers. God knew this would happen and that it would complicate matters, but in His own purposes it was better this way than to allow Isaac to be born sooner. God can work around our lack of faith, but it is easier on everyone if we trust Him rather than our own efforts.
23 Abraham obeys in faith and immediately has himself and every male in his household circumcised. This painful process can take weeks to heal. Yet, Abraham knows that obedience to God will have a reward that far outweighs the temporary pain obedience can cause.

Symbolically, circumcision represents the cutting away of sin. It can be painful and undesirable in our minds, but the eternal benefits we receive far outweigh the temporary pleasures that sin gives.