bi on nareneun hyeongwan badageul jaju sseureoya hae.

Both are possible, but they are slightly different.

• 비 오는 날 = a day when it is raining / a rainy day
• 비 온 날 = a day when it rained

In real life, 비 온 날 often suggests that rain has fallen and, as a result, the entrance floor is dirty or wet. That matches this sentence well, because tracked-in water or dirt is the reason you need to sweep.

So the sentence is focusing a bit more on the result of the rain than just the weather description.

비가 온 날 is also correct. In Korean, particles are often omitted when the meaning is still clear, especially in common expressions.

So these are both natural:

• 비가 온 날에는 ...
• 비 온 날에는 ...

The shorter version sounds very natural in everyday Korean. This kind of omission happens a lot, especially with weather expressions like 비 오다.

에는 is 에 + 는.

• 에 marks the time: on / in / at
• 는 adds a topic or contrast feeling

So 날에는 means something like:

• on days like that
• as for rainy days
• when it rains, at least...

The 는 gives a slight contrast nuance, as if the speaker is setting up a condition: On rainy days, you need to sweep the entrance floor often.

If you said 비 온 날에, it would still be understandable, but 비 온 날에는 sounds more natural when introducing a general rule or habit.

온 is the modifier form of 오다 in the past.

Here is the pattern:

• 오다 = to come
• 온 = that came / that has come

In the weather expression 비 오다, it means to rain. So:

• 비 온 날 literally = the day rain came naturally = the day it rained / a rainy day

This is an example of a verb modifying a noun:

• 온 modifies 날

현관 means the entryway / entrance area / foyer of a home or building. 바닥 means floor.

So 현관 바닥 means:

• the entrance floor
• the floor in the entryway

In Korean homes, the 현관 is often the area right inside the door where people take off shoes, so it is a place that easily gets dirty on rainy days.

Because 쓸다 is a transitive verb here, and the thing being swept is the object.

• 현관 바닥을 쓸다 = to sweep the entrance floor

So -을/를 marks what is being swept.

You could also hear:

• 현관을 쓸다 = to sweep the entrance area

But 현관 바닥을 쓸다 is a bit more specific, since what you actually sweep is the floor.

It comes from:

• 쓸다 = to sweep
• -어야 하다 = have to / must / need to

So:

• 쓸다 → 쓸어야 하다
• casual form: 쓸어야 해

This means:

• have to sweep
• need to sweep

The -어야 하다 pattern is one of the most common ways to express necessity in Korean.

This is because of Korean verb conjugation with ㅡ.

쓸다 has the stem 쓸-. When -어 is added, the ㅡ sound changes according to normal conjugation rules, giving:

• 쓸다 → 쓸어

So:

• 쓸어
• 쓸어요
• 쓸어야 해

This is just a form you need to get used to, much like:

• 쓰다 → 써
• 크다 → 커

Yes. 해 is casual speech.

Here are the main levels:

• 쓸어야 해 = casual
• 쓸어야 해요 = polite everyday speech
• 쓸어야 합니다 = formal

So the full sentence can become:

• 비 온 날에는 현관 바닥을 자주 쓸어야 해요.
• 비 온 날에는 현관 바닥을 자주 쓸어야 합니다.

자주 means often / frequently.

In this sentence, it modifies 쓸어야 해:

• 현관 바닥을 자주 쓸어야 해
• you have to sweep the entrance floor often

Its position is fairly flexible, but this placement is very natural. For example, these are also possible:

• 비 온 날에는 자주 현관 바닥을 쓸어야 해.
• 비 온 날에는 현관 바닥을 쓸어야 해, 자주.

The original sentence is the most neutral and natural version.

It usually means have to / need to / must, but in everyday conversation it can sound less harsh than English must.

Depending on context, it can feel like:

• a practical necessity
• common-sense advice
• a household rule

So in this sentence, it most naturally means something like:

• You need to sweep the entrance floor often on rainy days
• You should really sweep the entrance floor often on rainy days

It is stronger than a simple suggestion, but not necessarily as forceful as an order.

Korean often uses a singular noun for a general category.

So:

• 비 온 날에는 literally looks like on a day when it rained
• but naturally it means on rainy days or whenever it rains

This is very normal in Korean. The sentence is talking about a general situation, not just one specific day.