What was the nation of Israel supposed to become if they were obedient?
The obedient nation of Israel was to become a kingdom of priests, a nation of priests. A priest is described as a go-between between man and God. Israel was therefore to serve in that mediating role between God and humanity, according to the context.
Les explains that God says the nation of Israel is to be a kingdom of priests. He asks what a priest is and defines a priest as a go-between between man and God. So, if the nation was obedient, it was to become a nation of priests. Les also stresses that the kingdom is the kingdom unless the text designates something else. He notes that Grace Age believers are members of the kingdom, which is in heaven, but the kingdom is coming back to the earth. Near the end he turns to Acts 2:38, where Peter tells the house of Israel to repent and be baptized, every one of them.