Coherence and Unity in writing an essay

[Rezafo]

As you know coherence and Unity are the two key elements for a successful essay. But honestly I can’t find a clear-cut distinction between them, and I feel that they are almost the same.
Unity means oneness and we should not be led astray from the main idea and talk irrelevantly which does not support the topic.
Coherence means that with the help of transitions and clear explanation of each idea in our writing we try to create links which help the readers move smoothly from idea to idea within the paragraph.
Can you illustrate the difference between them so that I have a better and clearer concept?

My second question, the word “concept” I used above is so close in meaning to “conception”. How would you briefly demonstrate their subtle difference and usage?

[Jack_Rose]

Hey,

I would choose "concept" as you did?

Concept: more about idea for something

Conception: more about belief.

Sincerely,

J

[Tdol]

Coherence is the mechanics of connecting things together so that they flow nicely.

Unity is good in an essay. We must not waffle. Don't bring in irrelevant ideas. Support your topic.

This shows unity, but it's messy and hard to read because it lacks coherence. Why don't you have a go at turning it into something coherent that someone might read?