Final answer:
4) Transition. The speaker uses a transition when indicating that the forthcoming explanation will aid in understanding the rest of the speech. Transitions act as signposts to assist the audience in following the structure of the speech and distinguishing it from other rhetorical devices.
Step-by-step explanation:
When a speaker says, "What I am going to explain now will help you understand the rest of the speech," the device being used is a transition. Transitions are signpost language elements within a speech or writing that help the audience follow along by indicating a shift from one idea or section to another. This is distinct from a metaphor or simile, which are both rhetorical devices that create comparisons between different things. A metaphor asserts that one thing is another, while a simile uses the words "like" or "as" to compare. Rhetorical questions are used to engage the audience and encourage thought without expecting an answer. An anecdote is a short personal story. In the context given, the speaker is using a transition to guide listeners into a new segment of the speech, ensuring clarity and preparing the audience for the information that is to come.