What's the meaning of "降らば" in this sentence "降らば降れと天をにらみつけ"?


When listening to amazarashi's song "つじつま合わせに生まれた僕等" on Youtube, the first
"誦読" part has such a sentence "降らば降れと天をにらみつけ."

Intuitively, It sounds like a causative-conditional conjugation to me and
means something like "if it befalls on us." But I'm not sure. Can anybody out
there shed some light on it?

Many thanks.

[![enter image description
here](https://i.stack.imgur.com/v1AHT.png)](https://i.stack.imgur.com/v1AHT.png)

Edit:

First of all, thanks @naruto for the reply. And after digging around for a
while, I found 2 pieces of information that might also be useful to future
readers of this post.

Here are the links for reference:
<[link1](https://kobun.weblio.jp/content/%E3%81%B0)> and
<[link2](http://sanpunkobun.seesaa.net/article/300682150.html)>

By the way, I like this tiny part of the info:

[![enter image description
here](https://i.stack.imgur.com/DnufI.png)](https://i.stack.imgur.com/DnufI.png)




降らば降れ is the same as 降るなら降れ, but said using the grammar of classical Japanese.
A literal translation of this is "(O Rain,) if (you) fall, fall!". A message
like "Rain cannot stop me" is implied.

Conditional forms worked a little differently in classical Japanese. The
conditional ば attached to the 未然 (aka irrealis or pre-nai) form of the verb.
See: [using 未然形 and 已然形 with conditional
ば](https://japanese.stackexchange.com/q/80193/5010) and [寄らば from
寄らば大樹の陰](https://japanese.stackexchange.com/q/52173/5010)

In modern Japanese, this is a pattern that is used in stilted sentences and
has an implication of "let it go" or "I don't care". Similar expressions
include:

  * 死なば死ね: Let them die if necessary; I don't mind if they/you/I die
  * 笑わば笑え: If they laugh at me, let them do so (I don't care)




降らば降れ is the same as 降るなら降れ, but said using the grammar of classical Japanese.
A literal translation of this is "(O Rain,) if (you) fall, fall!". A message
like "Rain cannot stop me" is implied.

Conditional forms worked a little differently in classical Japanese. The
conditional ば attached to the 未然 (aka irrealis or pre-nai) form of the verb.
See: [using 未然形 and 已然形 with conditional
ば](https://japanese.stackexchange.com/q/80193/5010) and [寄らば from
寄らば大樹の陰](https://japanese.stackexchange.com/q/52173/5010)

In modern Japanese, this is a pattern that is used in stilted sentences and
has an implication of "let it go" or "I don't care". Similar expressions
include:

  * 死なば死ね: Let them die if necessary; I don't mind if they/you/I die
  * 笑わば笑え: If they laugh at me, let them do so (I don't care)

