This pattern uses こと as a nominalizer, turning the verb into a noun phrase, and then adds だ or はない to indicate obligation or lack thereof. It is often used in more formal or written contexts, and carries a sense of duty or necessity. When used in the affirmative (ことだ), it means there is a need to do something, often as a recommendation or rule. In the negative (ことはない), it means there is no need to do something, offering reassurance or dismissing a worry.

Note that this こと is the same spelling as the nominalizer こと used to turn verbs into nouns (e.g., 食べることが好きです). In this pattern, however, it combines with だ or はない to express obligation. The meaning should be clear from context, but be aware that ことがある can also mean 'there are times when' when used with the plain non-past form (e.g., 行くことがある means 'there are times when I go'), so pay attention to the form.