Det er vigtigere at hvile sig end at gå på arbejde, når man er syg.

Here det is a formal subject, similar to English it in sentences like It is important to rest.

So:

• Det er vigtigere ... = It is more important ...

The word det does not refer to a specific thing. It is just there because Danish often needs a subject in this kind of sentence.

A very literal breakdown would be:

• Det er vigtigere at hvile sig ...
  It is more important to rest ...

Vigtigere is the comparative form of vigtig (important).

So:

• vigtig = important
• vigtigere = more important
• vigtigst = most important

In this sentence:

• Det er vigtigere at hvile sig end at gå på arbejde
  = It is more important to rest than to go to work

This works much like English important → more important.

End means than in comparisons.

So:

• vigtigere ... end ... = more important ... than ...

In the sentence:

• at hvile sig end at gå på arbejde
  = to rest than to go to work

This is a very common pattern in Danish:

• større end = bigger than
• bedre end = better than
• vigtigere end = more important than

Because both are infinitives.

• at hvile sig = to rest
• at gå på arbejde = to go to work

After a comparison like vigtigere ... end ..., Danish often uses matching infinitive phrases on both sides:

• at hvile sig
• at gå på arbejde

This is similar to natural English:

• to rest rather than to go to work

In English, the second to is sometimes omitted, but in Danish it is very normal to keep at with both infinitives.

Because hvile sig is a common reflexive expression meaning to rest.

• hvile by itself can mean something like rest, repose, or be resting
• hvile sig means rest oneself, which is the natural everyday way to say rest

The reflexive pronoun changes with the subject:

• jeg hviler mig = I rest
• du hviler dig = you rest
• han/hun hviler sig = he/she rests
• man hviler sig = one/people rest

So in this sentence, sig matches man later in the sentence as the general person being talked about.

Sig is a reflexive pronoun, meaning the action goes back to the subject.

Here it is like oneself in English:

• hvile sig = rest oneself

English usually just says rest, but Danish often uses the reflexive form.

So:

• at hvile sig = to rest

Not every reflexive verb translates literally into English, so it is best to learn hvile sig as one unit.

Gå på arbejde is the normal Danish expression for go to work.

Literally, it looks like:

• gå = go/walk
• på arbejde = on/at work

But as a whole, it means:

• gå på arbejde = go to work

This is an idiomatic expression, so it is best learned as a chunk.

Related examples:

• jeg er på arbejde = I am at work / I’m working
• jeg skal på arbejde = I have to go to work

Because arbejde here is being used in a general, idiomatic way, not to mean a job as one specific noun.

Compare:

• på arbejde = at work / going to work
• et arbejde = a job / a piece of work

So in this sentence, arbejde is part of the fixed expression gå på arbejde, not a countable noun with an article.

Here når means when in the sense of whenever or in the situation where.

So:

• når man er syg = when one is sick / when you are sick

Why not hvis?

• når is used for something seen as a general or recurring situation
• hvis is more like if

This sentence states a general truth:

• When you are sick, it is more important to rest than to go to work

So når is the natural choice.

Very roughly:

• Når man er syg, ... = When one is sick, ...
• Hvis man bliver syg i morgen, ... = If one gets sick tomorrow, ...

No. Man here does not mean a man.

It means one, people, or informal English you in a general sense.

So:

• når man er syg = when one is sick / when you are sick

This is a very common Danish way to talk about people in general.

Examples:

• Man skal spise sundt. = One should eat healthy / You should eat healthy.
• Man lærer langsomt. = One learns slowly / You learn slowly.

Because syg is an adjective, not a noun.

In:

• man er syg

the structure is:

• man = subject
• er = is
• syg = sick

This is exactly like English is sick.

You only use an article with a noun, for example:

• Han er en patient. = He is a patient.

But with an adjective:

• Han er syg. = He is sick.

Yes, absolutely.

You can say:

• Det er vigtigere at hvile sig end at gå på arbejde, når man er syg.

or:

• Når man er syg, er det vigtigere at hvile sig end at gå på arbejde.

Both mean the same thing.

But notice the word order in the second version:

• Når man er syg, er det ...

In Danish main clauses, the finite verb usually comes in second position. So when the når-clause comes first, er must come before det.

That is an important Danish word-order pattern.

It expresses a general rule or general advice, not a specific person.

That is mainly shown by:

• man = one / people / you in general
• når = when / whenever

So the sentence means something like:

• In general, when people are sick, resting is more important than going to work.

If you wanted to talk about a specific person, you would usually use something like du, han, hun, or a name instead.

The sentence can be divided like this:

• Det er vigtigere = It is more important
• at hvile sig = to rest
• end at gå på arbejde = than to go to work
• når man er syg = when one is sick / when you are sick

So the overall pattern is:

• It is more important [to do X] than [to do Y] when [situation].

This is a useful structure you can reuse, for example:

• Det er bedre at blive hjemme end at tage af sted, når man er træt.
  = It is better to stay home than to leave when you are tired.