asita ha mise ga yasumi desu.

Because 明日 is a time word, and many common time expressions can be used without に.

So 明日は is natural and means as for tomorrow.

Some time words often appear without に, such as:

• 今日
• 明日
• 昨日
• 毎日

If you added に, it would usually sound unnatural here.

は marks the topic of the sentence.

So 明日は means something like:

• as for tomorrow
• regarding tomorrow

It sets the time frame first, and then the rest of the sentence tells you what is true in that time frame.

So the structure is:

• 明日は = as for tomorrow
• 店が休みです = the store is closed

When は is used as a particle, it is pronounced wa, not ha.

So:

• 明日は is read ashita wa

This is one of the first pronunciation exceptions learners meet in Japanese.

Here, が marks 店 as the grammatical subject of 休みです.

So the sentence is structured like:

• As for tomorrow, the store is closed.

The topic is already 明日, so 店 is marked with が inside that topic frame.

If you said 店は, that would make 店 a topic too, which often adds a contrastive feeling, like:

• As for tomorrow, the store is closed
  maybe implying something else is not

So 店が休みです is a very natural way to say this.

Yes, very often.

They do different jobs:

• は marks the topic
• が marks the subject

In this sentence:

• 明日 is the topic
• 店 is the subject

So there is no problem at all with having both:

• 明日は 店が 休みです

This is a very common pattern in Japanese.

休み is a noun, but in sentences like this it functions like a predicate with です.

So 店が休みです literally feels closer to:

• the store is on a rest/day off

But in natural English, that becomes:

• the store is closed

This is common in Japanese: a noun can be followed by です to describe a state.

Because 休み does not just mean that the door is shut. It often means the business is not operating, off for the day, or closed for business.

That is slightly different from words like 閉まっています, which focus more on the state of being shut.

So:

• 店が休みです = the store is closed / not open for business
• 店が閉まっています = the store is shut

In many situations, 休みです is the more natural choice for a shop, office, clinic, and so on.

Japanese does not have articles like a or the.

So 店 can mean:

• a store
• the store
• the shop

The exact meaning depends on context.

English requires an article, but Japanese does not.

です makes the sentence polite.

So:

• 明日は店が休みです = polite
• 明日は店が休みだ = plain
• 明日、店休み = very casual

In normal conversation with people you are not close to, です is the safe choice.

Yes, to some extent. Japanese word order is more flexible than English, as long as the particles still show the roles clearly.

For example, these are possible in the right context:

• 店は明日休みです
• 明日は店が休みです

They do not feel exactly the same, because the topic/focus changes.

Your original sentence puts tomorrow first as the topic, which is very natural if the main point is the schedule for tomorrow.

No. Standard Japanese is normally written without spaces between words.

So this would usually be written as:

• 明日は店が休みです。

Spaces are often added in beginner materials to make the sentence easier to read.

It is read:

• あした は みせ が やすみ です

Or more naturally, without pauses:

• あしたは みせが やすみです

A few useful reading notes:

• 明日 = あした
• 店 = みせ
• 休み = やすみ
• the particle は is pronounced wa