>The rain falls on the just and the unjust.

I didn't vote for this answer because 1. Frankly, I didn't expect this to be the most upvoted answer. 2. I wasn't really certain about the meaning of the Farsi proverb. But it seems (after a bit of googling) that my earlier [suggestion][1]; *collective punishment*, hit closer to home. 

**Rain is not a punishment**, and according to several [sources](https://www.google.it/search?q=rain+blessing+of+allah&tbm=isch&tbo=u&source=univ&sa=X&ved=0ahUKEwjWtejx5KPTAhVJB8AKHXkwDc0QsAQIKg&biw=1242&bih=580); [here][2] and [here][3], it is in actual fact a blessing, and all the more so in arid areas. 

A [comment][4] posted by @xDaizu, contained the following citation:

>This is one of the few New Testament verses that depicts God as commander of nature. Schweizer notes that **in Palestine rain was extremely important** and beneficial, the hot sun, was less so.

The focus of the proverb is on the innocent who, through the fault of a few wrong doers,  share and suffer the same penance unnecessarily. That is, the good (green/wet wood) burn alongside the bad (the dry wood). This may not be so tragic if you believe in the afterlife, but for the majority of Anglophones, and many devotees of the monotheistic Christian god (I'm going out on a limb here) this type of passivity and acceptance of *[God's will][5]* is no longer professed or tolerated.


  [1]: https://english.stackexchange.com/questions/383790/english-equivalent-of-the-persian-proverb-when-theres-fire-wet-and-dry-burn-t/384095#384095
  [2]: http://scanislam.com/articles/the-blessings-rulings-concerning-rains/
  [3]: https://www.islam21c.com/islamic-law/rain-a-summary-of-key-islamic-manners-and-rulings-part-1/
  [4]: https://english.stackexchange.com/questions/383790/english-equivalent-of-the-persian-proverb-when-theres-fire-wet-and-dry-burn-t#comment903561_383825
  [5]: http://www.biblestudytools.com/blogs/chris-russell/8-keys-to-knowing-god-s-will-for-your-life.html