NOT A TEACHER
Do you wish to know the function of sentences with the passive voice?
Well, one of the main functions is that the speaker/writer does not have to mention the doer of the action. In your example sentence about "the old kirk was built before ever the Pilgrims set sail for America," you can see that it is not necessary to know who built the old kirk.
Another reason that people use the passive is that since it leaves out the doer, it is often more neutral: Compare: "Someone in this office stole my cellphone yesterday" and "My cellphone was stolen yesterday." In the latter sentence, you are simply stating a fact without mentioning the alleged doer. It is more diplomatic than the first sentence.