Learn Hardcore Norwegian: Møtet er viktig, derfor kommer jeg tidlig. - The meeting is important, therefore I arrive early.

Derfor is an adverb meaning therefore. It links two independent main clauses and signals a cause–effect relationship: because the meeting is important, the speaker comes early. Although it behaves like a conjunction in meaning, it remains an adverb in Norwegian.

Why is there a comma before derfor, and can I omit it?

In standard written Norwegian you place a comma before an adverbial linker like derfor when it connects two main clauses.

It clarifies clause boundaries.
In very informal writing or run-on speech you might see it omitted, but it’s best practice to include it in formal texts.

Why does kommer (the verb) come before jeg (the subject) in the second clause?

Norwegian follows the V2 (verb-second) word-order rule:

The first element in the clause is derfor (an adverbial).
The finite verb kommer must occupy the second position.
The subject jeg then follows the verb.
If you start with the subject instead, you revert to the usual SVO order:
• Jeg kommer tidlig fordi møtet er viktig.

What form is møtet, and how do you form the definite singular of møte?

Møtet is the definite singular of the neuter noun møte (a meeting).
Neuter nouns in Norwegian form their definite singular by adding -et: et møte → møtet.

Why is viktig not inflected with -e or -t here?

Because viktig is used predicatively after the verb er. Predicative adjectives do not take agreement endings in Norwegian.
If you use the adjective attributively with a definite noun, you would add -e:
• det viktige møtet

What part of speech is tidlig, and does it get an adverbial ending like English -ly?

Tidlig functions as an adverb here, modifying kommer. In Norwegian many adverbs share the same form as their adjectives, so there is no extra -t or -ly.