The introduction is sometimes called the hook because it is supposed to grab the attention of the listener. The main points are sometimes referred to as hooks because they are supposed to serve as suitable hardware for hanging the preacher’s thoughts on.
I don’t use the word hook for either. Please don’t think I am being petty. I just think there are better things to aim for in both areas:
1. Introduction. The introduction to a sermon should grab the attention of the listener, but there is so much more to be achieved here. The introduction should stir motivation in the listener for listening to the preacher, for reading the passage, and for listening to the message. Simply arresting attention is a very inadequate introduction. I keep hearing messages that start with an engaging or humorous story (great! Attention grabbed!) and then an awkward transition to the message. Don’t be satisfied with just getting their attention, aim to stir their motivation.
2. Points. The points of a message are the skeleton of the strategy that you use to deliver your main idea and its relevance to your listeners. The goal is for them to encounter God as they have an encounter with God’s Word. But what happens when we start to think in terms of “hooks to hang thoughts on” … ? Well, listeners start to assume their task is to remember the outline of your message. In the same way as a handout tends to turn the preaching moment into a classroom lesson, so memorable hooks tend to make the listeners into learners. As Haddon Robinson used to say, your outline is for you, not for them. Make your points complete thoughts, full ideas, that develop and progress the communication of the main idea of the message. Maybe you need a memory aid to simplify your task as a preacher, then have simplified bullet points, but don’t make memorizing those points the point of listening to your sermon.
You can hook your listeners and then give them nice hooks to hang thoughts on if you like, but I wonder if the terminology might inadvertently (or even, advertently – what is the opposite?) lead to preaching that arrests attention but fails to stir motivation, and then offers memorable outlines for future reflection, while wasting golden opportunty for meaningful encounter in the present.