Abraham's on the road again in this chapter, which has to fit tightly between the promise given in Genesis 18 and the closing events here with the birth of Isaac. After all, along with the promise, Abraham was circumcised, and the promise was that the promised son would come within about a year. So you've got just a few months that this could happen during.
Abraham travels to the Negev, which is the wilderness just outside of the more fertile areas of the Promised Land. And there, he replays his behavior from Egypt earlier in the story (see Genesis 12:10-20). God again protects both Abraham and Sarah, though Abraham again puts them at risk with his choices.
God, however, protects them despite the repeat offense. He defends Sarah and her honor, and through this His promise is protected. What do we do with this story?
First, we take note that Abraham's new name does not make him perfect. His covenant with God still relies on God's grace, because he still struggles with the same fear-motivated sins from earlier in his life. That's good news for any of us repeaters, is not? Not that we should take this as an excuse not to change our behaviors, but that we can take it as evidence of grace.
And, honestly, if you get into sin every time you travel, maybe you should rethink your decision-making paradigm about travel?
Second, we can see the faithfulness of God. God made a promise. It will be held by the power of God, not the faithfulness (or lack thereof) of a man. God's promises are delivered by Him.
Third, we can see one other thing that should alarm us: all of Abimelech's household fell under judgment because of one sin.
The section wraps up with the birth of Isaac and his subsequent circumcision. We are reminded that Abraham was 100 years old at the time, and that Sarah and Abraham knew just how impossible this was without God's intervention. The reading pauses here, with the feast for the weaning of Isaac.
Trouble, though, waits around the corner.