What's the point of using "stare" in the passive voice?

Question

I can't get why stare should be used in the passive voice after essere. Look at these examples:La macchina è stata riparata da Max;La carrozzeria è stata rifatta;Due camicie sono state lavate;My book says:"The passive voice in Italian consists of a form of essere plus the past participle, which agrees in gender and number with the subject of the sentence". It doesn't explain why stare is necessary.

Answer 1

It is not stare, but essere. The past participle is the same for both essere and stare. So in this case

è stata riparata = it was repaired v.

ha riparata = it repaired

in Italian, only certain verbs can be used with essere in passato prossimo - so in order to make this sentence sound the way we want it to, we must use :

è stata riparata, as you cannot say è riparata, this means nothing and sounds like an adjective rather than past participle.

Answer 2

I think it's just past tense (from what little I remember from my days taking Italian!)