biga waseo changmuneul dada dueosseoyo.

It means because it’s raining or since it rained depending on context.

• 비가 오다 is the standard Korean expression for to rain.
  • Even though 오다 usually means to come, in 비가 오다 it means rain falls / it rains.
• 와서 is from 오다
  • -아서/-어서.
• In this sentence, -아서/-어서 gives a reason/cause:
  Because it was raining, ...

So:

• 비가 와서 창문을 닫아 두었어요
  = Because it was raining, I closed the window and left it closed.

Because -가 marks 비 as the subject of the clause.

• 비가 오다 = rain falls / it rains
• Here, the sentence is simply stating the cause: rain was falling

If you used 비는, it would sound more contrastive or topical, like:

• As for the rain, ...
• The rain, though, ...

That is not the basic neutral meaning here. So 비가 와서 is the most natural form.

Yes, 오다 normally means to come, but Korean uses certain noun + verb combinations that work like fixed expressions.

One of the most common is:

• 비가 오다 = to rain

Other weather expressions work similarly:

• 눈이 오다 = to snow

So you should learn 비가 오다 as a set expression, not as literally rain comes in everyday translation.

It means I closed the window and left it that way or I had closed the window in advance.

This part is built from:

• 창문을 = the window
  • object marker -을
• 닫다 = to close
• -아/어 두다 = to do something and leave it in that state / do it in advance
• 두었어요 = past polite form of 두다

So 닫아 두었어요 is more than just closed. It implies:

1. the action was completed, and
2. the result remained in place afterward.

In other words, the window is understood to be still closed.

This is a very common learner question, and the difference is important.

• 닫았어요 = I closed it
• 닫아 두었어요 = I closed it and left it closed / I closed it in preparation

So -아/어 두다 adds a nuance of:

• preparation
• keeping the result
• doing something for later convenience or necessity

Examples:

• 창문을 닫았어요
  = I closed the window.
• 창문을 닫아 두었어요
  = I closed the window and left it closed, probably because there was a reason to do so.

In your sentence, that reason is the rain.

It can feel a little mixed in English, but here is the idea:

• 와서 does not itself strongly mark tense in this kind of connection.
• 두었어요 is past tense.

So the action of closing happened in the past, but the result may still matter now.

A natural interpretation is:

• Because it was raining, I closed the window and left it closed.

Depending on context, it could also feel like:

• It was raining, so I had closed the window.
• Since it was raining, I closed the window.

Korean often focuses less on matching English-style tense in every clause and more on the relationship between events.

Here it means because / so, but -아서/-어서 can also simply connect actions as and then in other sentences.

In this sentence, it clearly expresses a reason:

• 비가 와서
  = because it was raining

That is because the second clause is a reasonable response to the first clause:

• rain happened
• so the window was closed

So while -아서/-어서 does not always have to mean because, that is the natural reading here.

Because 창문 is the thing being acted on.

• 닫다 = to close
• The thing you close takes the object particle:
  • 창문을 닫다 = to close the window
  • 문을 닫다 = to close the door

So 창문을 is simply the direct object of 닫아 두었어요.

By itself, 두다 often means to put or to place. But after another verb in the form -아/어 두다, it becomes an auxiliary-like construction.

In that pattern, it means something like:

• do and leave as is
• do in advance
• keep something in that resulting state

So:

• 닫아 두다 = close it and leave it closed
• 켜 두다 = turn it on and leave it on
• 열어 두다 = open it and leave it open
• 써 두다 = write it down in advance

This is a very useful pattern in everyday Korean.

Because this is the polite informal speech level, which is extremely common in everyday Korean.

The final verb is:

• 두었어요

This makes the whole sentence polite but not overly formal.

Compare:

• 닫아 두었어요 = polite everyday style
• 닫아 두었습니다 = more formal
• 닫아 뒀어 = casual speech

So the sentence is suitable for normal conversation with someone you should speak politely to.

Yes. In everyday speech, 두었어요 is very often contracted to 뒀어요.

So these mean essentially the same thing:

• 창문을 닫아 두었어요
• 창문을 닫아 뒀어요

The uncontracted form may look a bit clearer to learners, while the contracted form is extremely common in real speech.

The Korean word order is:

• 비가 와서 = because it was raining
• 창문을 = the window
• 닫아 두었어요 = closed and left it closed

So literally it is something like:

• Because rain came, the window (I) closed-and-left.

A more natural English rendering is:

• Because it was raining, I closed the window and left it closed.

Korean often puts the reason first, then the object, and the main verb at the end.

Yes, but that is completely normal in Korean.

The sentence does not explicitly say I, but it is understood from context. In English, we usually need to say the subject, but Korean often omits it when it is obvious.

So:

• 비가 와서 창문을 닫아 두었어요

  naturally implies:

• Because it was raining, I closed the window and left it closed.

Depending on context, it could theoretically be we or someone else, but I is the most natural default in many situations.