Learn Hardcore Japanese: isya ni ha, kaze no yobou no tame ni, tearai to sinkokyuu wo komame ni suru you ni iwaremasita. - The doctor told me to wash my hands and take deep breaths frequently to prevent colds.

Keeps に’s role as “by / from the doctor” (agent of the passive).
Uses は to make “as for the doctor / from the doctor” the topic, often with a nuance of contrast or emphasis, like:
- “(At least) the doctor told me to do X.”
- “The doctor (in particular) told me to do X.”

You cannot replace this with 医者は言われました; that would be ungrammatical, because 言われました is passive and needs the agent with に.

Who is the subject of this sentence? Why is 私 not written?

The subject is understood to be 私 (I / me), but it is omitted, which is very normal in Japanese.

The full, non-omitted version would be:

私は、医者には、風邪の予防のために、手洗いと深呼吸をこまめにするように言われました。
→ (I was told by the doctor to frequently wash my hands and take deep breaths to prevent colds.)

Japanese drops pronouns like 私 whenever they are clear from context. Here:

言われました is passive past.
With 医者に as the agent, the natural subject is “I” (the one who was told).

So 私 is left out as unnecessary.

Why is 言われました used (passive), instead of 言いました?

言われました is the polite past passive of 言う.

言いました – I / someone said (something).
言われました – I / someone was told (something).

Because the meaning is “I was told by the doctor”, Japanese uses the passive:

医者に言われました。
→ I was told by the doctor.

If you said:

医者は、手洗いと深呼吸をこまめにするように言いました。

this would mean:

The doctor said to do frequent handwashing and deep breathing.

That focuses on what the doctor said, not on what I was told. The given sentence focuses on the speaker being on the receiving end of the advice, which is why the passive 言われました is used.

What does the pattern 〜するように言われました mean?

The pattern is:

[plain-form verb] + ように + 言う / 言われる

Here: するように言われました.

It means “to be told to do X” or “to be told that one should do X”.

So:

手洗いと深呼吸をこまめにするように言われました。
→ I was told to wash my hands and do deep breathing frequently.

Some important points:

The verb before ように is plain non-past (する, not しました).
ように言う can be translated as “tell someone to do / not to do” in an indirect, instruction/request sense.
The passive 言われました makes it “I was told to do 〜”.

Compare:

医者に、手を洗いなさいと言われました。
– I was told, “Wash your hands.” (more direct command style)
医者に、手を洗うように言われました。
– I was told to wash my hands. (more neutral/indirect)

What does こまめに mean, and how is it different from just よく or たくさん?

こまめに is an adverb meaning roughly:

frequently, regularly, diligently, without neglect

It has a nuance of:

Doing something at proper intervals,
Being attentive and consistent,
Not being lazy or skipping it.

So:

手洗いをこまめにする
→ wash your hands frequently / regularly (as you should).

Comparisons:

よく手を洗う – wash your hands often / well (quite general).
たくさん手を洗う – sounds odd; たくさん is more about quantity.
こまめに手を洗う – wash your hands regularly and diligently; don’t slack off.

With health advice, こまめに is very common and sounds natural and slightly “responsible” or “careful.”

Why is it 風邪の予防のために and not 風邪を予防するために? Are both correct?

Both are grammatically correct, but the structure is different.

風邪の予防のために
- 風邪の予防 – prevention of colds (noun phrase)
- 〜のために – for the purpose of ~
Literally: “for the sake of prevention of colds.”
Pattern:
- [Noun] + の + ために → for the sake of / for the purpose of [Noun]
風邪を予防するために
- 風邪を予防する – to prevent colds (verb phrase)
- 〜ために – in order to ~
Literally: “in order to prevent colds.”
Pattern:
- [plain-form verb] + ために → in order to [do verb]

Nuance:

風邪の予防のために sounds a bit more nouny / formal / written, using 予防 as a noun.
風邪を予防するために is a little more directly action-focused (verb).

In everyday speech, you will hear both, and the meaning is effectively the same here.

Why is there only one を after 深呼吸, even though we have 手洗いと深呼吸?

This is a common pattern in Japanese: when multiple nouns share the same case particle, the particle often appears only once, after the last item.

A と B をする → do A and B (both are direct objects of する)

Here:

手洗い – handwashing
深呼吸 – deep breathing
手洗いと深呼吸をする – do handwashing and deep breathing

You could also say:

手洗いをして、深呼吸をします。

but 手洗いと深呼吸をする is shorter and equally natural, especially when both are する-nouns.

So を after 深呼吸 covers both 手洗い and 深呼吸 as the objects of する.

What exactly are 手洗い and 深呼吸 grammatically? Why do they use する?

Both 手洗い and 深呼吸 are noun forms of actions (often called verbal nouns or する-nouns).

手洗い
- Literally: hand-washing
- A noun: the act of washing hands
- Used with する:
  - 手洗いをする – to wash (one’s) hands
深呼吸
- Literally: deep breathing
- Also a noun: the act of deep breathing / taking deep breaths
- Used with する:
  - 深呼吸をする – to take deep breaths / to do deep breathing

So 手洗いと深呼吸をこまめにする is:

(do) handwashing and deep breathing frequently.

This Noun + を + する pattern is very common with many actions in Japanese.

What does 〜のために mean here? Is it “because of” or “in order to”?

ために can mean either:

for the sake of / in order to (purpose), or
because of / due to (reason/cause),

depending on context.

In this sentence:

風邪の予防のために clearly expresses purpose:
→ for the purpose of preventing colds / in order to prevent colds.

So here it is “in order to / for the sake of”, not “because of.”

If it were a reason meaning “because of a cold”, it would normally look different, e.g.:

風邪のために学校を休みました。
→ I stayed home from school because of a cold.

There are many に’s: 医者には, ために, するように. Do they all have the same role?

They are the same particle に, but used in different standard patterns:

医者には
- Here に marks the agent in a passive sentence:
  - 医者に言われました。 – I was told by the doctor.
- は just adds topical/contrast emphasis on that agent.
風邪の予防のために
- ために is a fixed pattern meaning “for the sake of / in order to”.
- The に is part of the ために construction expressing purpose.
するように言われました
- ように is another fixed pattern: [verb + ように] expresses a manner / way / aim, and with 言う, it expresses telling/asking someone to do something.
- So here に is part of ように, not an independent particle.

So:

医者に → agent of passive
ために → purpose
ように → “so that / to (do) …” as part of the ように言う pattern

They are the same particle に, but in different fixed constructions.