siken no mae ni, daizina pointo dake yomikaesimasu

試験の前に means before the exam.

• 試験 = exam
• 前 = front / before
• の links 試験 and 前, so 試験の前 literally means the exam’s before, or more natural English, the time before the exam
• に marks the time point when the main action happens

So the structure is:

[event/time] の 前 に = before [event/time]

A useful point: 前 is a noun in Japanese, not a preposition like English before.

大事 is a na-adjective.

That means:

• before a noun, it takes な
• at the end of a sentence, it does not use い

So:

• 大事なポイント = important points
• このポイントは大事です = this point is important

This is different from an i-adjective like 高い:

• 高い山 = a tall mountain

So 大事な is correct because 大事 belongs to the na-adjective group.

Here, ポイント means points, key points, or main ideas.

It comes from the English word point, but in Japanese it is often used for:

• important ideas in notes or a textbook
• key test topics
• main takeaways

So in this sentence, 大事なポイント means something like:

• the important points
• the key points

It does not mean a physical point or dot here.

だけ means only.

So:

• 大事なポイントだけ = only the important points

It limits what is being reread. The speaker is saying they do not reread everything—just the important parts.

Compare:

• 大事なポイントを読み返します = I reread the important points
• 大事なポイントだけ読み返します = I reread only the important points

Good question. In Japanese, だけ often attaches directly to the noun, and the object marker may be omitted or appear after だけ.

So all of these are possible:

• 大事なポイントだけ読み返します
• 大事なポイントだけを読み返します

Both mean basically the same thing here.

The version without を is very common and natural in everyday Japanese. So the sentence is completely normal as written.

読み返します means reread or read again.

It comes from:

• 読む = to read
• 返す when used as part of a verb can add the sense of doing again/back

So:

• 読みます = read
• 読み返します = reread / go back and read again

In this sentence, that nuance matters. The speaker is probably reviewing material they have already read before.

読み返します is the polite non-past form.

It is used when speaking politely or in neutral standard Japanese.

The non-past form in Japanese can mean:

• a habitual action: I usually reread
• a future action: I will reread
• a general practice: I reread

In this sentence, it most naturally sounds like a habit or usual practice: Before an exam, I reread only the important points.

The plain form would be:

• 読み返す

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

So even though English usually needs I, Japanese does not have to say it.

This sentence could be understood as:

• I reread only the important points before an exam
• or, depending on context, we/you/they reread...

But in a normal standalone example, learners usually understand the hidden subject as I.

If you wanted to include it, you could say:

• 私は試験の前に、大事なポイントだけ読み返します。

That is correct, but often unnecessary.

The basic order is:

[time expression] + [object] + [verb]

So here:

• 試験の前に = before the exam
• 大事なポイントだけ = only the important points
• 読み返します = reread

Japanese verbs usually come at the end of the sentence.

A very literal breakdown would be:

Before the exam, only the important points, I reread.

Natural English changes the order, but Japanese keeps the verb at the end.

Yes, 試験前に is also possible.

• 試験の前に = before the exam
• 試験前に = before the exam

Both are natural, but they feel slightly different in structure:

• 試験の前に uses the regular noun pattern A の 前
• 試験前 is more like a compact compound expression, similar to pre-exam

For learners, 試験の前に is often easier to understand because the grammar is more transparent.