“Wherefore I also said” - Rather because ye have done the things mentioned in Judges 2:2, “I have now said (i. e. I now protest and declare) that I will not drive them out from before you” (compare Judges 19:29). And it was the annonncement of this resolution by the Angel that caused the people to weep.
The word thorns in this verse is supplied by the King James Version from the similar passage in Joshua (see the marginal reference). Other versions adopt a different reading of the original text, and prefer the sense “they shall be to you for adversaries” (compare the last words of Numbers 33:55).