This is common with this type of a verb (known as a copula) in many languages. With these sentences, the subject is often a matter of perspective (the guests are women, the women are guests). Verbs like "to be" are like this.
Here is an example in Esperanto:
La gastoj estas virinoj = The guests are women (no words are in the accusative case, and no actions are happening to either noun)
La virino manĝas gaston = The women eats a guest (gaston is in the accusative as an action is happening to it)