Genesis 18

1 The location appears to have been a sacred place for the Canaanites near Hebron (Wycliffe).
2 Eventually it would be revealed that the leader of this threesome was God in human form. However, it is not indicated that Abraham knew this immediately. The code of hospitality was highly regarded in much of the region, so it was common for someone to welcome strangers into his home. Abraham went to great extremes to accommodate the strangers. This is probably a reflection of the goodness in his heart brought about by his relationship with God.

Abraham was wealthy and important in the region, yet he humbly welcomed the strangers. It is always more polite to be humble in the presence of others.

4 It is interesting to see that Abraham offers a little bread and water when he intends to prepare a feast for the strangers.

Any stranger that had been traveling on foot all day would appreciate the offer to refresh himself with a little food, quick wash, and a short rest.

6 Sarah was to make bread out of the best flour they had.
7 Abraham serves up his best calf. This is very extravagant.
8 The mixture of curdled and fresh milk was served to sustain the guests while the main meal was being prepared. As they were eating the main meal, Abraham stood by to make sure that all their needs were being met.
9 Conversation usually accompanied meals, and Sarah was one of the topics of discussion.
10 This visitation must have happened within a few months of Gen 17:21. Abraham may not have revealed his previous encounter with God to Sarah, but now Sarah would hear the same prophecy herself.
12 On the surface, Sarah's response appears to be similar to Abraham's response (Gen 17:17). However, from the reaction of the strangers it is apparent that Sarah laughed in unbelief while Abraham had laughed in amazement.
14 There is nothing too miraculous for God. He created the universe and its various "laws of nature," and He can overrule the natural order as suits His purpose. He can intervene any time He wishes to encourage His people or judge the hopelessly ungodly by extraordinary means.
15 Sarah needlessly lies to cover her embarrassment, but the Stranger (i.e., God) makes sure she knows that she can not hide even her thoughts from Him.