Learn Hardcore Japanese: kansya no kimoti wo kaita messeezi wo yomu to, aite mo kitto genki ni natte iku desyou. - When someone reads a message filled with gratitude, they will surely start to feel better.

感謝の気持ちを書いた = “(someone) wrote their feelings of gratitude (in it)”
感謝の気持ちを書いたメッセージ = “a message (in which someone) wrote their feelings of gratitude”
→ “a message expressing gratitude.”

The subject (who wrote the message) is omitted and understood from context.

Why is 書いた in the past tense when the whole sentence is talking about the future (…元気になっていくでしょう)?

Japanese relative clauses (verb phrases that modify nouns) use the tense that fits that action, not the main clause.

書いたメッセージ = “a message that was written / that has been written”
→ The writing is already completed when the message is read.

The future-like part is in 元気になっていくでしょう (“will gradually become energetic / feel better”).

So the timeline is:

Someone writes the message (書いた).
Later, someone reads it (読むと).
As a result, the other person will (from then on) become more cheerful (元気になっていくでしょう).

Past in the modifier (書いた) + future-like in the main statement (なっていくでしょう) is completely normal.

Why are there two を particles? What does each を belong to?

The sentence has two different verbs, and each verb has its own を:

感謝の気持ち を 書いたメッセージ
- を marks 感謝の気持ち as the object of 書いた (wrote).
- “(someone) wrote feelings of gratitude.”
メッセージ を 読むと
- を marks メッセージ as the object of 読む (read).
- “(someone) reads the message.”

Japanese allows multiple を in a sentence as long as each belongs to a different verb phrase.

What does と after 読む mean here? Is it a quotation marker or something else?

Here 読むと uses と as a conditional particle, not a quotation marker.

Vると … often means “when / whenever (someone) does V, … happens.”

So:

メッセージを読むと、相手も…元気になっていくでしょう。
= “When (someone) reads the message, the other person will also surely start to feel better.”

Nuance compared to some other conditionals:

Vると often implies a fairly automatic or natural result.
Vたら is more general “if / when,” and can be more speaker-controlled or event-like.

Here, 読むと suggests that reading naturally leads to the result (the other person becoming more cheerful).

Who is the subject of 読む and 元気になっていく? There’s no I, you, or they.

Japanese often omits pronouns when they are clear from context.

For 読む (to read):
The implied subject is something like “you”, “the person”, or “one”—whoever is reading that message. It depends on the broader context.
For 元気になっていく:
The explicit noun 相手 (“the other person,” “the person on the other side,” “the recipient”) is the subject.
So structurally it’s:
- (When you / someone) reads a message expressing gratitude, the other person (相手) will also surely gradually become cheerful.

Japanese does not repeat pronouns like English; it relies on context and the closest appropriate noun (here, 相手 for the becoming-元気 part).

What is the nuance of 相手も? What does も add here?

相手 = the other person / the person you’re dealing with.
も = “also, too, even.”

相手も suggests:

“the other person also,” “the other person too.”

So the nuance is something like:

Not only you (or not only the writer/reader), the other person as well will become cheerful.

It implies there is someone already feeling good, or at least emphasizes that the effect extends to the other person too.

Why is it 元気に and not 元気を or just 元気 before なる?

With なる, you normally mark the new state or condition with に:

Noun + に + なる
な-adjective + に + なる
い-adjective + く + なる

元気 is a na-adjective (元気な人), so:

元気になる = “become healthy / cheerful / energetic.”

You cannot say 元気をなる.
Just 元気なる is ungrammatical in standard Japanese; you need に for this pattern.

Examples:

先生になる – become a teacher
きれいになる – become pretty/clean
上手になる – become skillful
暑くなる – become hot (い-adjective → く)

What is the nuance of なっていく compared to just なる?

なる alone simply states a change of state:

元気になる = “become/feel better,” “get energetic.”

〜ていく adds the idea of change progressing over time or moving forward into the future.

元気になっていく implies “will gradually become more cheerful / will keep getting better from now on.”

So:

元気になるでしょう = They will (at some point) feel better.
元気になっていくでしょう = They will go on becoming more and more cheerful; their mood will improve over time, not just at a single moment.

It gives a softer, more gradual, and future-oriented feeling.

What does きっと add to the sentence? Is it strong or weak?

きっと is an adverb meaning something like:

“surely,” “certainly,” “I’m pretty sure,” “in all likelihood.”

In this sentence:

相手もきっと元気になっていくでしょう。
→ “The other person will surely gradually feel better as well.”

Combined with でしょう (which already softens the statement into a polite guess), きっと expresses a fairly strong expectation, but still as a prediction, not as a guarantee. It’s confident but not absolute.

What is the function of でしょう here?

でしょう has two main roles:

Conjecture / probability:
It shows that the speaker is predicting or guessing rather than stating a hard fact.
Politeness / softness:
It softens the statement, making it less direct and more polite or considerate.

So:

元気になっていく。
= “(They) will become cheerful.” (fairly direct, could sound blunt depending on context)
元気になっていくでしょう。
= “(They) will probably / surely become cheerful.”
“I expect they will become cheerful.”

Here, with きっと, it becomes a polite, confident prediction:
“The other person will surely start to feel better.”