8:3 thirty thousand. Since only twelve thousand men were in Ai (Joshua 8:25), it seems that such a large force may have been unnecessary, especially when augmented by five thousand more lying in ambush between Bethel and Ai (Joshua 8:12), and another large army led by Joshua on another side of the city (Joshua 8:13). It may be that Joshua did not know the number of armed men in Ai, or it may be that he wanted a large force available in event the nearby allied city of Bethel would decide to enter the fight. In any case, the mission was accomplished; the city and all its inhabitants were destroyed, as God had commanded.
8:28 Ai. The location of Ai is controversial. Liberal scholars have alleged that a mound traditionally identified as Ai had been destroyed long before Joshua’s time, and was not even inhabited at the assumed time of the conquest. On the other hand, modern conservative archaeologists have argued that a much more likely location for Ai has been discovered, the history of which apparently appears fit the Biblical account. However, the actual chronology of the conquest itself is still uncertain.
8:28 for ever. Ai was evidently reoccupied at a later date (note Nehemiah 7:32). Joshua had intended to destroy it so totally that it would never be rebuilt, and it was still desolate at the time the book of Joshua was written. The Hebrew word for “for ever” (olam) basically means a very long time, with no foreseeable end.