I found a sentence from a test:
That evils had power was believed in the olden days.
Why did the writer use the passive voice in this example? What difference would it have made if the sentence had been the following?
People used to believe that evils had power in the olden days
What you have is a noun clause that begins with that.
That-clause as a noun clause
A that-clause is an example of a noun clause. It can be the subject or the object of the verb.
The that-clause is "that evils had power" and the given sentence (in OP) is grammatical. Such a construction might not be used as frequently as others. For example, one might instead write
The idea that evils had power was believed in the olden days.
When talking about a fact, one could use "the fact" instead of "the idea".
Another example would be
It was believed in the olden days that evils had power.
