Explanation:

- Sum and substance is an idiom often used to portray the main point or the essential part of something. It distills everything down to the core idea or most important aspect.

- Option 1: Essence - This closely aligns with the idiom. Essence refers to the fundamental nature or most important quality of something.

- Option 2: Difficulty - This doesn't match with the idiom. Difficulty refers to something that is hard to accomplish or deal with.

- Option 3: Deliberation - This is about carefully considering or thinking about something, not related to the key point of the idiom.

- Option 4: Assessment - Refers to evaluating or estimating the nature of something, rather than summarizing its core.

- Correct Answer: Option 1 - Essence