I’m not sure what to make of the telelogical exegetical principle. The application Greg makes comes awfully near to “the end justifies the means.” Regardless, I completely agree with Greg’s conclusion:
Divinely sanctioned nationalistic violence [in the Old Testament era] initially looked like it could establish the Kingdom of God, but it failed. The nation of Israel tried to live by the sword but it ended up dying by the sword (as Jesus said would always happen). …
This negative object lesson laid the groundwork for the coming of the anti-nationalistic, anti-violent Kingdom, inaugurated through Jesus.
I think the Bible records a very human striving after God, and after the otherworldly ethos of God. That process involved much trial and error, and the painful lessons of personal and corporate experience.
The Old and New Testaments, together, teach that violence begets violence (though I don’t concede that God ever approved of genocide); whereas the non-violent resistance practised by Jesus wrought God’s victory.
This is the lesson believers ought to take away from scripture; any other reading is sub-Christian.