What shift takes place in who is reading the words from Anne's diary and why did the author choose to do that?

It changes the mood from somebody who is curious about what's written in the diary (Mr. Frank) to somebody who is eager to tell a story (Anne Frank).

The author chose to do that in order to let the audience know what it's like to be reading another person's diary from what it's like to write a diary, as in Anne's case. It also allows the audience to know the actual date and setting when Anne started writing the diary.

Explanation:

The question above is related to the drama entitled, "The Diary of Anne Frank."

It can be seen in Line 59 that Mr. Frank started reading Anne's Diary. This was after Miep told him that there were letters and notes in the bundles of paper that she gave him.

As Mr Frank was reading, his voice shifted to Anne's voice. This was the time she talked about his father's business and how her family went into hiding.