biga waseo gabangi jeojeosseoyo.

오다 means to come, but it is also used for weather phenomena like rain and snow. So 비가 오다 literally means rain comes, but naturally it means it rains.

When 오다 is connected with -아서/-어서, it becomes 와서:

• 오다 → 와서

So 비가 와서 means because it rained or it rained, so...

In this sentence, -아서/-어서 connects two clauses and shows a reason or cause.

• 비가 와서 = because it rained
• 가방이 젖었어요 = the bag got wet

So the whole sentence means:

• It rained, so the bag got wet
• Because it rained, the bag got wet

This ending can also sometimes just show sequence, but here the meaning is clearly cause and result.

가 is the subject marker, and here it simply identifies 비 (rain) as the subject of the clause.

• 비가 와서 = because rain came / because it rained

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

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

That is not the neutral feeling of this sentence. 비가 is the most natural choice here.

Because 젖다 is an intransitive verb. It means to get wet or to become wet.

That means the bag is not a direct object; it is the thing that changed state. So it takes 이/가, not 을/를:

• 가방이 젖었어요 = the bag got wet

If you want a transitive idea like something made the bag wet, Korean usually uses a different verb, such as 적시다:

• 비가 가방을 적셨어요 = The rain soaked the bag

So with 젖다, 가방이 is correct.

젖었어요 is the past form of 젖다.

• 젖다 = to get wet
• 젖어요 = gets wet / is getting wet
• 젖었어요 = got wet / became wet

The sentence describes a completed result:

• It rained
• As a result, the bag got wet

So the past tense sounds natural. It is talking about what happened, not a general truth.

In Korean, when clauses are linked with -아서/-어서, tense is normally shown on the final verb, not on both verbs.

So:

• 비가 와서 가방이 젖었어요

already tells you that the whole event happened in the past because the final verb is 젖었어요.

Korean usually does not say:

• 비가 왔어서 가방이 젖었어요

in ordinary speech for this meaning. The normal pattern is to leave the first verb in the connective form and mark tense at the end.

젖다 usually means to get wet or to become wet, not simply to be wet as a static description.

So:

• 가방이 젖었어요 = The bag got wet

If you just want to describe something as wet, Korean often uses adjectives/descriptive verbs such as 축축하다 depending on context. But 젖다 strongly suggests that something became wet through some cause.

That is why it fits very naturally after 비가 와서.

Because there are really two clauses:

1. 비가 와서
2. 가방이 젖었어요

Each clause has its own subject:

• 비가 = rain is the subject of 오다
• 가방이 = bag is the subject of 젖다

This is completely normal in Korean. English learners sometimes expect only one subject in a sentence, but Korean often has separate subjects for separate clauses.

By itself, 가방이 just means the bag or a bag, depending on context.

In real Korean, possession is often omitted when it is obvious. So if you are talking about your own bag, 가방이 젖었어요 can naturally mean:

• My bag got wet

Korean does not need to say 내 가방이 unless the speaker wants to emphasize whose bag it was.

Yes. That is also very natural.

• 비가 와서 가방이 젖었어요 = It rained, so the bag got wet
• 비 때문에 가방이 젖었어요 = The bag got wet because of the rain

The difference is small:

• 비가 와서 focuses on the event it rained
• 비 때문에 focuses on the rain as the cause

Both are common and correct.

젖었어요 is in the polite informal style, often called the -아요/-어요 style.

• 젖었어요 = polite
• 젖었어 = casual/plain spoken style
• 젖었습니다 = more formal polite style

So the whole sentence is polite and natural for everyday conversation.

Yes, but the most natural reading here is cause.

Because rain and a wet bag have a very obvious cause-and-effect relationship, most listeners will understand:

• Because it rained, the bag got wet

Technically, -아서/-어서 can sometimes connect events in a way that feels like and then, but in this sentence the causal meaning is much stronger.