Learn Hardcore Japanese: mainiti undou wo surukoto ha kenkou no tame ni taisetu desu. - Exercising every day is important for your health.

毎日運動します。
= I exercise every day. (normal sentence with a verb)
毎日運動をすることは健康のために大切です。
= The act of exercising every day is important for your health.
Here, 毎日運動をすること is like saying “exercising every day” as a thing.

In Japanese, to say “X is important / easy / difficult / fun / my hobby”, you usually need to make X into a noun:

食べる → 食べること (eating)
勉強する → 勉強すること (studying)
運動する → 運動すること (exercising)

So すること is necessary because the sentence is not saying “I exercise”; it’s saying “Exercising (every day) is important.”

Could we say 毎日運動します instead of 毎日運動をすることは〜? What’s the difference in meaning?

They express different ideas:

毎日運動します。
= I exercise every day.
→ A statement about what (someone) does.
毎日運動をすることは健康のために大切です。
= Exercising every day is important for your health.
→ A general statement about the importance of that habit.

The original sentence is not describing someone’s actual routine; it’s making a general, objective comment about what is important for health. That’s why it needs the 〜することは〜です pattern (a noun-like subject + predicate), not just a simple “I do X” form.

Why is it 運動をすること and not just 運動すること? Is を necessary?

With する-verbs like 運動する, 勉強する, 料理する, the object marker を is often optional.

運動する = to exercise
運動をする = also to exercise

So both:

毎日運動することは〜
毎日運動をすることは〜

are grammatically correct and natural.

Nuance:

運動する feels a bit more compact and is very common in speech.
運動をする can feel slightly more explicit or textbook-like: “to do exercise”.

In many modern contexts, natives probably say 毎日運動することは… more often, but the version with を is perfectly fine and often taught to learners, especially early on.

Why do we have ことは and not ことが? What’s the difference between 〜ことは大切です and 〜ことが大切です?

Both are grammatically possible, but there is a nuance:

〜ことは大切です。
は marks the topic: “As for doing X, (it) is important.”
→ Sounds like a general, comment-style statement. Very natural here.
〜ことが大切です。
が marks the subject: “It is doing X that is important.”
→ Highlights “what is important is X (rather than something else).”

In a sentence like:

毎日運動をすることは健康のために大切です。

は sets “exercising every day” as the thing we’re talking about and then comments “it is important for health.” This fits the neutral, explanatory tone of the sentence.

You could say 〜ことが大切です, especially if you want to contrast it with other possibilities (e.g., “Not just dieting, it’s exercising every day that is important”). But the textbook-style general statement commonly uses は.

What does の do in 健康のために? Why not just 健康ために?

の connects 健康 (“health”) to ため (“sake, benefit, purpose”) and makes the fixed pattern:

Noun + の + ため(に) = “for the sake of Noun; for Noun; for the benefit of Noun”

So:

健康のため(に)
literally: “for the sake of health”

Without の, 健康ために is ungrammatical. You need の to link the noun and ため:

家族のために = for my family
勉強のために = for study / for the sake of studying
仕事のために = for work
健康のために = for health

Think of の here as working like “of” or a possessive/connecting “’s” in English:
“for the sake of health” / “for health’s sake.”

Why is it ために and not just ため? What role does に play here?

ため by itself is a noun meaning “sake, benefit, reason.”
To use it as a purpose phrase in a sentence, it normally takes the particle に:

健康のために運動します。
= I exercise for my health.
日本語の勉強のために日本に行きました。
= I went to Japan for the purpose of studying Japanese.

In 健康のために大切です, 健康のために modifies 大切です:
“(It is) important for health.”

In many casual contexts, the に after ため can sometimes be dropped, but the form 〜のために is the standard and is what textbooks teach. Dropping に here (健康のため大切です) would sound a bit stiff or written; 健康のために大切です is the natural, neutral form.

What exactly does 大切です mean here? Is it the same as “important”? How is it different from 重要です or いいです?

In this sentence, 大切です does mean “is important”, but it often carries a nuance of value / care / something you should cherish or take seriously.

Rough comparison:

大切です
- important in the sense of “something you should take good care of / value”
- often used for health, relationships, time, promises, etc.
- 毎日運動をすることは健康のために大切です。
  = Exercising every day is important (something you should value) for your health.
重要です
- “important” in a more formal, academic, or logical way
- common in news, business, lectures, documents
- 毎日運動をすることは健康のために重要です。
  = also correct, but sounds more formal / technical.
いいです
- “good”
- 毎日運動をすることは健康にいいです。
  = Exercising every day is good for your health.
- Focuses more on the positive effect, not on “You should treat this as important.”

So 大切です fits very well with the idea of “this is something you should value and not neglect.”

Could I say 毎日運動をするは健康のために大切です without こと? Why is こと necessary?

You cannot say 毎日運動をするは…. That is ungrammatical.

In Japanese, an entire verb phrase like 毎日運動をする (to exercise every day) cannot directly take は (or が) as if it were a simple noun. You must first turn the verb phrase into a noun-like unit using こと or の:

毎日運動をすることは〜
毎日運動をするのは〜 (more casual)

So:

✗ 毎日運動をするは健康のために大切です。
✓ 毎日運動をすることは健康のために大切です。
✓ 毎日運動をするのは健康のために大切です。(more spoken-feeling)

The こと (or の) is what allows the whole action “exercising every day” to act as the topic of the sentence.

Where does 毎日 attach? Does it modify 運動, する, or the whole clause?

毎日 is an adverb of time, and here it modifies the action “to exercise”:

毎日 [運動をする] こと
= the act of [exercising every day]

In practice, you can think of it as modifying the verb phrase 運動をする as a whole:

毎日運動をする = to exercise every day

It does not mean “everyday health” or “daily health”. It’s about how often you do the exercising, not what kind of health you have.

Could we change the word order, like 健康のために毎日運動をすることは大切です? How flexible is the order in this sentence?

Yes, you can rearrange some parts without changing the basic meaning. For example:

毎日運動をすることは健康のために大切です。
健康のために毎日運動をすることは大切です。
毎日運動をすることは大切です。健康のために。 (more spoken, split into two)

All are understandable. Japanese word order is generally [topic] + [information about it], and the role of each phrase is marked by particles (は, を, の, に, etc.), not rigid word order.

But:

Keeping は early is natural: 〜ことは〜です.
Keeping 健康のために right before 大切です feels very smooth:
“is important for health.”

So the original order is very typical and natural, but modest reordering like 健康のために毎日運動をすることは大切です is also fine.

What’s the difference between 健康のために大切です and something like 健康にいいです? Could we say 毎日運動をすることは健康に大切です?

健康のために大切です
= It is important for (the sake of) health.
→ Focuses on importance as a measure to protect/maintain health.
健康にいいです
= It is good for your health.
→ Focuses on the beneficial effect on health.

You cannot say 健康に大切です in this context; 大切 doesn’t combine with に that way. Instead:

X は健康のために大切です。
X は健康にいいです。
X は健康に悪いです。 (bad for your health)

So you could make a parallel sentence:

毎日運動をすることは健康にいいです。
= Exercising every day is good for your health.

But if you want to use 大切, it needs 健康のために, not 健康に.