naeil hoeuiga isseoseo iljjik jayagessda.

Here, -아서 / -어서 connects two clauses and means something like because or so.

• 내일 회의가 있어서 = because there is a meeting tomorrow
• 일찍 자야겠다 = I should go to bed early

So in this sentence, 있어서 gives the reason for the speaker’s decision.

A useful comparison:

• 비가 와서 집에 있었어요. = Because it rained, I stayed home.
• 시험이 있어서 공부해요. = I’m studying because I have an exam.

In this sentence, 있다 does not mean to exist in a very abstract sense; it means to have / there is in the sense that a meeting is scheduled.

회의가 있다 is the normal Korean pattern for there is a meeting or I have a meeting.

So:

• 회의가 있다 = to have a meeting scheduled / there is a meeting
• not 회의를 있다, which is ungrammatical

The particle 가 marks 회의 as the thing that exists.

This is a very common structure:

• 약속이 있어요. = I have an appointment / plan.
• 수업이 있어요. = I have class.
• 회의가 있어요. = I have a meeting.

Even though English says I have a meeting, Korean often uses the existence structure instead.

자야겠다 comes from:

• 자다 = to sleep
• -아/어야 하다 = must / have to / should
• -겠다 = often expresses the speaker’s judgment, realization, or intention

So 자야겠다 means something like:

• I should sleep
• I’d better go to bed
• Looks like I need to sleep

In this sentence, a very natural translation is:

• I should go to bed early.
• I’d better get to bed early.

It sounds like the speaker is deciding this on the spot or realizing it for a practical reason.

Both can be translated as I have to sleep / I should sleep, but they feel a little different.

• 자야 해요: more direct, factual obligation
  
  • I have to sleep.
• 자야겠어요 / 자야겠다: the speaker’s own conclusion, realization, or decision
  
  • I should sleep / I’d better sleep.

So:

• 내일 회의가 있어서 일찍 자야 해요.
  = I have to sleep early because I have a meeting tomorrow.
• 내일 회의가 있어서 일찍 자야겠다.
  = I’ve got a meeting tomorrow, so I should get to bed early.

The version with -겠다 often sounds a bit more like the speaker is thinking it through and deciding.

In Korean, -겠다 does not only mean future tense. It often expresses:

• the speaker’s intention
• a guess or judgment
• a realization
• a decision

So in 자야겠다, -겠다 is not just will sleep. It is more like:

• I guess I should sleep
• I’d better sleep
• I’ll have to sleep

That is why -겠다 is common in self-talk or spontaneous decisions:

• 이제 가봐야겠다. = I should get going now.
• 공부해야겠다. = I should study.
• 좀 쉬어야겠다. = I should get some rest.

일찍 means early.

In this sentence, it modifies 자야겠다:

• 일찍 자야겠다 = should sleep early / should go to bed early

Some useful comparisons:

• 일찍 일어났어요. = I woke up early.
• 일찍 왔어요. = I came early.
• 오늘은 일찍 자고 싶어요. = I want to sleep early today.

English often says go to bed early, while Korean simply says sleep early in many cases.

Korean often omits the subject when it is clear from context.

In 내일 회의가 있어서 일찍 자야겠다, the subject is understood as I because:

• the speaker is talking about their own meeting
• 자야겠다 sounds like the speaker’s own decision or realization

So even without 저는, the sentence naturally means:

• I should go to bed early because I have a meeting tomorrow.

You could add the subject if needed:

• 저는 내일 회의가 있어서 일찍 자야겠어요.

But in everyday Korean, leaving it out is very normal.

Yes.

The base verb is 있다. When you attach -어서, it becomes 있어서.

Breakdown:

• 있다 = to exist / to have
• 있어서 = because there is / because I have

This kind of conjugation is very common:

• 가다 → 가서 = go and / because went
• 먹다 → 먹어서 = eat and / because ate
• 아프다 → 아파서 = because it hurts / because I’m sick
• 있다 → 있어서 = because there is / because I have

So the first half literally works like:

• 내일 회의가 있어서 = because tomorrow there is a meeting

자야겠다 is a plain-style ending, so by itself it sounds casual or like self-directed speech.

It is natural in:

• talking to friends
• talking to yourself
• writing casually
• inner thoughts

If you want to make it polite, you would usually say:

• 내일 회의가 있어서 일찍 자야겠어요.

That sounds polite and natural in conversation.

A more formal style could be:

• 내일 회의가 있어서 일찍 자야겠습니다.

That sounds more formal or deliberate.

So the original sentence feels natural as casual spoken Korean.

Yes. That is one of the key nuances of -야겠다.

It does not only express outside obligation. It often sounds like:

• the speaker has realized something
• the speaker is making a practical decision
• the speaker is resolving to do something

So 내일 회의가 있어서 일찍 자야겠다 can feel like:

• Since I have a meeting tomorrow, I should get to bed early.
• I’d better go to bed early since I have a meeting tomorrow.

This sounds more personal and self-directed than a strict external command.

Yes, you can.

• 내일 회의가 있어서 = because I have a meeting tomorrow
• 내일은 회의가 있어서 = similar, but 내일은 adds slight topic emphasis, like as for tomorrow or tomorrow, you see

The version without 은 is simple and neutral.

The version with 은 may sound a little more contrastive depending on context, for example:

• 오늘은 괜찮은데 내일은 회의가 있어서 일찍 자야겠다.
  = Today is fine, but tomorrow I have a meeting, so I should sleep early.

So both are possible, but the original is the most straightforward.