A teacher needs to have something to teach. And that, at the very least  means having a main point or idea. This is what teachers hope that students get, if they don’t get anything else, from the class.

An idea usually comes in the form of a subject (what you want to talk about) and a compliment (what you want to say about the subject). For example, consider:

“Do not sharply rebuke an older man, but rather appeal to him as a father, to the younger men as brothers, the older women as mothers, and the younger women as sisters, in all purity” (1 Tim 5:1-3).

What is Paul talking about here? (the subject). We know that Paul is talking to Timothy about ministry in the church. Paul is telling Timothy how to treat others as he ministers to them. How should Timothy treat those in the church that he is ministering to? (what he has to say about the subject) He should treat them as he would his own family.

It is worth spending time working out an idea and working it into a complete sentence. The main idea in the text above is something like: As we minister to others in the church we should treat them as we would our own family.

Your class may be made up of many points or ideas. However, it is better to have one controlling or main idea that everything else supports, explains or applies to life. Try to focus the class on defending, explaining or applying one main point through a series of points. It is much more likely that students will believe, understand, and act on one point well made than several unrelated points.

Taken from Biblical Preaching by Haddon Robinson.