"He lifted his eyes and saw: And behold! Three men were standing before him…" (Genesis 18:2)
Rashi cites the famous teaching of the ancient Sages that the three men who came to Avraham were really three angels: (i) one to inform Sarah that she’d soon have a child, (ii) one to overturn Sodom, and (iii) one to heal Avraham.
An obvious question is asked here: Why did the second of the three angels come to Avraham’s home? Unlike the other two, his mission (ie. destroy Sodom) had nothing to do with Avraham, his home, his wife, or his family!
A famous answer proceeds as follows:The Midrash (Bereishis Rabbah 8:5) says that at the time of creation of humanity, the angels in heaven were divided in their assessment as to the wisdom of their creation.
One group of angels argued that a human being would have many fine points and that we’d make for a good creation. The other group disagreed, and was quick to point out that we’d have a tendency to be difficult, dishonest, hostile, etc.
Now, when the years passed and Sodom became an utterly wicked city, the second group of angels – those who had opposed the creation of Adam – were able to point to the behavior of Sodom as proof positive that their initial position had been correct!
As a result, when Hashem had to eventually destroy Sodom, He wanted to send a message to those angels in heaven who had been negative towards the creation of man. How did He do so?
He sent an angel to Avraham’s home – the same one who’d soon be charged with the destruction of Sodom.
In other words: yes, it is true – the one being sent to destroy Sodom didn’t really belong there! But Hashem wanted this angel to be able to relay a crucial message upon the completion of his mission.
Having seen Avraham Aveinu … and his family … and their sanctity … and what a human being could ultimately develop into and become … this angel would be able to speak to the negative group of angels and tell them that their outright negative position towards mankind was a grave error!