Justin Beadles with some helpful thoughts on why it's better to internalize rather than memorize your message (sermon, speech, etc.):
Unless you are a student competing in a division that requires such, there is no need to memorize your speech. You simply need to internalize it. This means you think through the flow and main idea enough that it becomes natural to recall. Memorizing and manuscripting are both unnecessary in my book. They take a colossal amount of time and, with rare exception, come off stilted and unfeeling.
Here is a tactic from the ancients that might help you internalize your next speech:
I think through all my speeches in terms of taking people on a tour of my house.
1. The Front Door: This is my introduction 2. The Living Room: My first point 3. The Dining Room: My second point 4. The Play Room: My conclusion
At any time I need only remember what room I am in and am then able to recall easily where the speech is headed. Try it and see.