Certain Spanish verbs are frequently used to construct Impersonal Expressions. When used in this manner, they may be referred to as Impersonal Verbs Sentences using Impersonal Verbs do not have a specific person or thing as the subject. In English we use the non-specific “it”, but in Spanish the pronoun is omitted.

es preciso - it's necessary
es urgente - it's urgent
es importante - it's important
es interesante - it's interesting
es malo - it's bad

The Impersonal Verb is usually followed by que. It is necessary to use the subjunctive form of the verb immediately following que.

Es importante que me avise.
It is important that you warn me.

Es menester que lo veas.
It's necessary that you see it.

Es urgente que lo veas.
It's urgent that you see it.

Es preciso que trabaje.
It is necessary that you work.

Note: An exception to the rules is made when the Impersonal Verb expresses certainty, as:

Es cierto que lo hará.
It is certain that he will do it.

Also, when the dependent verb has not its own subject, both the following constructions are correct:

Es necesario hacerlo.
It must be done.

Es necesario que se haga.
It must be done.