Why can't God cope with Iron chariots? One of the core beliefs of Judaism and Christianity is that God is
  omnipotent, able to do anything that is logically possible. But
  surprisingly, the Bible does not consistently support this idea ...
  there’s the following little-known Bible verse: “And the Lord was with
  Judah; and he drave out the inhabitants of the mountain; but could not
  drive out the inhabitants of the valley, because they had chariots of
  iron.” — Judges 1:19 Source


I think the quotation is self-explanatory. How is this verse understood by Christian apologists?
וַיְהִי יְהוָה אֶתּ־יְהוּדָה
  And the LORD was with Judah
  וַיֹרֶשׁ אֶת־הָהָר
  and he took possession of the hill [country]
  ...כִּ֣י לֹא לְהוֹרִישׁ אֶת־יֹשְׁבֵי הָעֵמֶק
  but he could not drive out those living in the valley...
  


The pronoun "he" in the final line is of interest. In fact, the Hebrew has no pronoun, nor does it have a form of "could". Technically, there is neither subject nor finite verb in the clause at all. The MT would be more formally translated using a dummy subject: "it was not possible to drive out...", as both Gesenius (§ 114l) and Jouon-Muraoka (§ 160, n. 14) have it.1 

The question remains: not possible for whom? There are at least two helpful comments that can be made from the Hebrew text that are not evident in English:


Line 3 is a dependent clause, subordinated to line 2 and constituting a concession ("...although it was not possible to drive out"); and
the English "took possession" and "drive out" are actually the same word: hôrish (~"dispossess"). 


For both reasons, the one who dispossesses in line 2 must be the same one who dispossesses in line 3. 

The identity of the subject of line 2 is best derived from the context:    


  v. 17: And Judah...defeated the Canaanites
  v. 18: Judah also captured Gaza
  v. 19: And the LORD was with Judah... and ? took possession but ? could not drive out...
  v. 20: And [Caleb] drove out from [Hebron] the three sons of Anak...
  v. 21: But the people of Benjamin did not drive out the Jebusites...
  v. 22: The house of Joseph also went up against Bethel, and the LORD was with them.


Notice who is doing the capturing, driving, defeating, etc: people. In every verse. Verse 20, in fact, repeats for a third time hôrish, and Caleb is the only possible subject. As the people go about their various aggressions, the LORD was with them. That's his role here (cf. v. 2).

It's clear, then, that it was Judah who was "unable to cope" with the iron chariots in v. 19. There is no suggestion of Yahweh being unable to accomplish his purpose here. Still, sensitive readers of the text, including (I should hope) Christian apologists, are likely to find the "exceptive" clause of v. 19 disquieting. 


  We are left to wonder why iron chariots should have proven so decisive if Yahweh was indeed with Judah as verse 19a says he was....There is something profoundly unsatisfying about the simple juxtaposition of the two statements in verse 19.... It is the beginning of a much more mixed picture of Israel’s military fortunes that will be revealed in the rest of the book.2 





1. The alternative, which most English translations appear to have adopted, is to add a form of יָכְלוּ = "they could", with the Greek (both versions), Targum, some Hebrew manuscripts, and the BHS apparatus. It's interesting that the grammarians seem to find the MT as written less objectionable than do the translators!



2. Barry G. Webb, The Book of Judges, NICOT; (Grand Rapids: Eerdmans, 2012), 108-109.