Final answer:
Betsy Read prevents Tim from delivering the letter because she fears for his safety, which is a common theme related to the protection of characters and the handling of sensitive information in historical narratives.
Step-by-step explanation:
Betsy Read stops Tim from delivering Mr. Heron's letter because she fears for Tim's safety. In historical novels or narratives that involve espionage or message delivery, characters often intercept or prevent the delivery of letters to protect the intended messenger.
The mention of a letter and its delivery is a common thematic element that involves the protection of characters, secrecy, and the potential for subterfuge. The interception or prevention may be due to the sensitive nature of the letter's contents or potential danger to the courier, thereby highlighting the protective instincts of characters like Betsy.