Learn Swedish: Vad du än väljer borde du tänka på det väsentliga. - Whatever you choose, you should think about the essential.

This is an example of substantivation, where an adjective acts as a noun. By pairing the neuter definite article det with the definite adjective väsentliga, you create an abstract concept meaning "the essential thing" or "that which is essential". You don't need a noun like sak (thing) because this grammatical structure handles it on its own.

If the concept is neuter singular (det), why doesn't the adjective end in -t (like väsentligt)?

Because it is in the definite form. Even though the abstract concept is neuter singular, the standalone definite article det forces the adjective to take its definite ending, which is almost always -a. You would only use the -t ending for an indefinite abstract concept, such as något väsentligt (something essential).

How does the phrase vad du än väljer work to mean "whatever you choose"?

In Swedish, you create "-ever" words by pairing a question word with the adverb än. For example, vad ... än (whatever), vem ... än (whoever), and var ... än (wherever). The subject and verb are placed between these two words, which is why the phrase is structured as vad du än väljer rather than grouping vad and än together.

Why is the word order borde du instead of du borde in the second half of the sentence?