Ik rust liever dan dat ik de sleutelpassage probeer.

Liever means rather or preferably. It is used when you are choosing one option over another.

So in this sentence, Ik rust liever ... means I would rather rest ...

A useful comparison:

• graag = gladly / with pleasure / like to
• liever = rather / prefer

For example:

• Ik rust graag. = I like resting / I rest gladly.
• Ik rust liever. = I’d rather rest.

Because rust is the conjugated verb form that agrees with ik.

• rusten = the infinitive, to rest
• ik rust = I rest / I am resting

In Dutch, you normally use the conjugated verb in a sentence with a subject:

• Ik rust.
• Wij rusten.

So Ik rust liever is the normal finite-clause form, not the infinitive form.

Dutch often uses the simple present with liever to express preference.

So:

• Ik rust liever = I’d rather rest

Even though English often uses would rather, Dutch does not need a special conditional form here.

If you want, Dutch can also use a more explicit conditional style:

• Ik zou liever rusten.

That also means I would rather rest, but Ik rust liever is perfectly normal.

Because liever is a comparative form, and Dutch normally uses dan after comparatives.

You can think of it like this:

• graag → liever
• good → better
• comparatives in Dutch are followed by dan

Examples:

• Ik drink liever thee dan koffie.
• Hij blijft liever thuis dan dat hij meegaat.

A common point for learners: Dutch uses dan for inequality/comparison, while als is used for equality.

• groter dan = bigger than
• even groot als = as big as

Because the second part is a full clause with its own subject and finite verb: ik de sleutelpassage probeer.

When liever is followed by a whole clause, Dutch commonly uses dan dat:

• Ik rust liever dan dat ik de sleutelpassage probeer.

But if what follows is just a noun or short phrase, you usually use only dan:

• Ik drink liever thee dan koffie.

So the pattern is roughly:

• liever + X dan Y for words or short phrases
• liever + clause dan dat + clause when the second option is a full clause

Because dat introduces a subordinate clause, and in Dutch subordinate clauses the finite verb usually goes to the end.

So:

• main clause: Ik rust liever
• subordinate clause: dat ik de sleutelpassage probeer

That is why you get:

• dan dat ik de sleutelpassage probeer

and not normal main-clause word order.

This is a very important Dutch pattern:

• Ik weet dat hij komt.
• Ze zegt dat ze moe is.
• ... dan dat ik de sleutelpassage probeer.

Sleutelpassage is a compound noun.

It is made from:

• sleutel = key
• passage = passage / section

Together it means something like key passage, crucial passage, or important section, depending on context.

Dutch very often writes compound nouns as one word, where English would often use two words. So:

• sleutelpassage
• treinstation
• boekenkast

This is completely normal Dutch spelling.

In Dutch compounds, the article is determined by the final part of the compound.

The final part here is passage, and passage is a de word. Therefore:

• de passage
• de sleutelpassage

This is a useful general rule:

• het boek → het studieboek
• de tafel → de keukentafel
• de passage → de sleutelpassage

Yes, it is grammatical and understandable.

The structure liever ... dan dat ... is standard Dutch, especially when you want to make a clear contrast between two actions.

That said, it can sound a little more deliberate or formal than a very casual everyday sentence. In casual speech, people might sometimes choose a simpler wording depending on context.

But as a model for grammar, it is perfectly good Dutch and shows an important pattern:

• preference with liever
• comparison with dan
• subordinate clause with dat
• verb at the end in the subordinate clause