Expresses an advice or recommendation; 'should', 'it is important', 'it is necessary'.
Long explanation:
The ~ことだ grammar point is used to express a piece of advice or a recommendation to someone. It can be translated as 'should', 'it is important', or 'it is necessary' in English. The formation differs depending on whether it is used with a verb, い-adjective, な-adjective, or noun.