And the LORD was with Judah, and he took possession of the hill country, but he could not drive out the inhabitants of the plain because they had chariots of iron.
At the first reading of this verse, it seems like the author of Judges is suggesting the iron may be too strong for God. In fact his point is totally the opposite. Prior to this incident the author of Judges tells us about the various victories over the Cananites that God gave the people of God, especially of the brutal Adoni-Bezek. God had done this just as He had promised the people after the death of Joshua. So there is no doubt that the God of Israel is omnipotent!
What is important to remember that it is God who has allowed this opposition to test His people, as he says later in Judges (See Judges 2:20 - 23). God is full of grace and because He is gracious he wants His people to be fully obedience to Him. And part of his preferred method for making us more obedient is to allow our disobedience to play out so that we see how much we need Him and repent! Judah failure to finish their conquest because of the opposition of the iron chariot is grace in action because their lack of trust in God is now exposed so that they should turn and repent before God.
May be you currently going through a period of divine frustration. God has allowed an “iron chariot” in your life that seems impregnable. You think the chariot is the problem. Have you considered whether God is allowing that “iron chariot” to bring you to the end of your faith so that your only dependence is on God? May of us are deluded in thinking we are following God when in fact we are only depending on ourselves. So we need to carefully examine our lives and see whether the problems we are facing are as a result of divine frustration!