raigetu no ryokou no tame ni, hoteru no yoyaku wo site okimasu.

Because の is doing noun-to-noun linking twice:

• 来月の旅行 = next month's trip / the trip next month
• ホテルの予約 = hotel reservation

In both cases, の connects one noun to another and makes the first noun modify the second.

So the sentence is built like this:

• 来月の旅行 = the trip
• 来月の旅行のために = for the sake of that trip / for that trip
• ホテルの予約 = a hotel reservation
• ホテルの予約をしておきます = I’ll make a hotel reservation in advance

来月の旅行 treats 旅行 as a noun and modifies it with 来月:

• 来月の旅行 = the trip next month

If you said 来月に旅行, that would feel incomplete, because 旅行 there is just sitting as a noun without being properly connected to the rest of the phrase.

You could say something like:

• 来月に旅行します = I will travel next month

But when 旅行 is itself the noun being described, 来月の旅行 is natural.

Here, 〜のために means for or for the sake of.

So:

• 来月の旅行のために = for next month’s trip

It shows the purpose or reason for the action.

In this sentence, the idea is:

• For next month’s trip, I’ll reserve a hotel in advance.

A small nuance point: ために can also mean because of in some contexts, but here it is clearly the purpose meaning.

The comma separates the purpose phrase from the main action:

• 来月の旅行のために、 = As for / for next month’s trip,
• ホテルの予約をしておきます。 = I’ll make a hotel reservation in advance.

It is not mandatory in every sentence, but it is very natural here because the opening phrase is a bit long. It helps readability.

Both are possible, but they are slightly different in structure.

• ホテルを予約する = reserve a hotel
• ホテルの予約をする = make a hotel reservation

The sentence uses the second pattern, where 予約 is treated as a noun and combined with する.

This noun + をする pattern is very common in Japanese:

• 勉強をする = do studying / study
• 準備をする = do preparation / prepare
• 予約をする = make a reservation

So ホテルの予約をしておきます is very natural.

〜ておく means doing something in advance or ahead of time, usually to prepare for something later.

So:

• 予約をします = I will make a reservation
• 予約をしておきます = I will make a reservation in advance

That fits perfectly with 来月の旅行のために, because the speaker is preparing now for a future trip.

This is one of the most important grammar points in the sentence.

The difference is preparation.

• ホテルの予約をします
  = I’ll reserve the hotel.
  This just states the action.

• ホテルの予約をしておきます
  = I’ll reserve the hotel in advance.
  This adds the idea of preparing beforehand.

So 〜ておく often implies:

• doing something before it becomes necessary
• taking care of something now
• being prepared

Because in 〜ておく, おく is functioning as an auxiliary expression, not as the full verb 置く meaning to put.

So in most everyday writing, it is usually written in kana:

• しておく
• 買っておく
• 確認しておく

This helps show that it is a grammar pattern meaning do in advance, not the literal verb put.

Japanese often leaves out the subject when it is understood from context.

So even though there is no explicit I, the sentence naturally means something like:

• I’ll make a hotel reservation in advance for next month’s trip.

Depending on context, it could also be we, but in isolation, English usually supplies I.

This omission is extremely common in Japanese.

Formally, しておきます is in the non-past polite form. In Japanese, the non-past can mean either:

• present/habitual, or
• future

Here, because of the context (next month’s trip), it is understood as future:

• I’ll make a hotel reservation in advance.

So even though Japanese does not have a separate future-tense verb form like English, the meaning is clearly future here.

Yes. In natural English, book the hotel or book a hotel is often the most natural translation.

The Japanese literally looks more like:

• make a hotel reservation in advance

But in smooth English, you might say:

• I’ll book a hotel in advance for next month’s trip.
• I’ll reserve a hotel in advance for next month’s trip.

So the Japanese structure and the most natural English wording do not have to match exactly.

Yes.

• 予約しておきます = I’ll make the reservation in advance.

  • the speaker states their intention or decision

• 予約しておきましょう = Let’s make the reservation in advance or I’ll go ahead and make the reservation

  • depending on context, it can sound like a suggestion or an offer

So 〜ます is a straightforward statement, while 〜ましょう brings in suggestion/volunteering nuance.

No. Normal Japanese writing does not use spaces between words.

This sentence would normally be written as:

来月の旅行のために、ホテルの予約をしておきます。

Spaces are often added only in learning materials to make the structure easier to see.