This is the 7914th most frequent Swedish word.
viktig
Important.
In this sentence, 'viktig' is used as an adjective to describe the abstract concept of importance of eating healthy food.
Det är viktigt att äta hälsosam mat.
It is important to eat healthy food.
Here, the word 'viktigaste' is a superlative form of 'viktig', emphasizing being honest as the utmost importance.
Den viktigaste saken är att vara ärlig.
The most important thing is to be honest.
In this instance, 'viktig' as an adjective indicates the significance of an individual within a group context.