The Lord appears to Abraham with three changes:
1. He changes His own name; that is, He reveals to Abram a new name, El Shaddi, God the Almighty, the one for whom nothing is impossible.
2. He changes Abram and Sarai's names to Abraham and Sarah, altering their identity although not changing it completely, but rather giving it a new shade or significance.
3. He changes the covenant, or rather expands its terms. Before their were two promises: many offspring, and possession of the land. Now there are three: many offspring, possession of the land, and a unique relationship between the offspring and God: they will be His people, and He will be their God. The covenant will be an everlasting covenant, extending from generation to generation. Therefore, a new sign is needed for the covenant, one which can be repeated for each generation, the sign of circumcision.

Throughout Abraham's journey God has been revealed as:
1. The Lord (who spoke, who appeared, whom he made an altar to, whom he called upon, and who made covenant with him)
2. El Elyon, God Most High, who gave him victory over Lot's oppressors and to whom he paid tithes through Melchizedek
3. El Shaddai, who promises a son in his old age through his wife in her old age and barreness. Abraham's first response to El Shaddai is to laugh! But he also responds with obedience: "that very day" he circumcised himself, his son Ishmael, and all the slaves in his household, both "born into it and bought with money."

Note 1: It is possible to be redeemed into the family of faith (bought with a price) and be a part of the covenant. The children of those who are so redeemed are (or can be) also part of the covenant.

Note 2: What happened to those men, the 300 or so who were in Abraham's household even before Ishmael was born? Did their descendants continue to serve Isaac and Jacob? If so, did they go down to Egypt under Joseph? Did they come up in the Exodus? By that time (six or more generations) they could have been a mighty host, if they were all given wives. Hmmmm...

Genesis 17:1