Rav Zevin: The connection between the seemingly polar opposite episodes of Avraham's welcoming guests at the beginning of the Parsha and Akeidat Yitzchak at the end of Parsha.
Why did the angel whose job was to destroy Sodom come to Avraham?
Why did Avraham keep davening for Sodom so many times? Did Avraham feel responsible for its destruction?
The difference between אפר (ashes) and עפר (dust) - past vs. future.
Netziv: Why is it that Avraham's willingness to sacrifice Yitzchak is specifically what showed that Avraham feared God?