“And if not, may fire go out from Abimelek and consume the leaders of Shekem and the house of Millo. Then, let fire go out from the leaders of Shekem and the house of Millo and consume Abimelek.”
Why fire? Sure, fire is a sign of judgment, but more importantly, fire is the only proper way to destroy the brambles (Psalm 58:9). Yet, when the brambles are choking out the forest, there is no good way of burning out the brambles without burning the trees as well. Such is the judgment of Jotham’s parable — he is essentially saying to them that if they think that what they have done is proper, then fine, God will be the judge, but if your conscience convicts you, then let your actions destroy you under God’s hand of wrath.
Paul writes much the same thing in Romans 1, when he speaks of God giving the people up to their sin and lust of their hearts. The point that Paul is making is that one of God’s forms of judgment is to allow people to pursue their lusts, removing his hand of restraint from them, for sin destroys us not only in eternity, but in this life as well. Did the leaders of Shekem know that what they were doing was wrong? Surely they must have. Did the people of whom Paul speaks know that what they were doing was wrong? Again, they must, that is the work of their conscience, yet how often (as Paul also points out) we suppress our conscience and the things that we know are right when we desire to pursue sin.
We sometimes talk about how much times change over the generations. And were we just simply talking about the application of technology, then we are entirely right to do so. My first computer, for example, had 16 Kilobytes of RAM, no hard drive, and took up my whole desktop. Today, I take my MacBook Pro wherever I go. But, if we are talking about human nature, very little has changed. We still are sinners to the core, we still think that the end justifies the means, and we still pursue what we think we want instead of what God thinks is best for us. We still wallow in our sin and are in desperate need of a savior.