Depending on how you sound, what you have to say may not matter.
Audiences won’t get anything out of your talk if they can’t hear you, don’t understand what you say, or stop listening. It may seem petty, but there are many reasons that audiences may tune you out based entirely on the way you sound. Are you talking too fast? Too quietly? Is your voice monotonous? Do you have an accent that gets in the way of your audience understanding you? Are you reading too much of what you have to say? It’s important to understand how you sound so that you can work to avoid making these mistake.
If you have the chance, consider recording yourself so you have a better idea of what you actually sound like. This can be as simple as making an audio recording of a practice run-through. But with video cameras becoming so easily available that they’re now a part of our cellphones, it’s almost as easy to make a video recording that you can use to evaluate both how you sound and what you look like. This is a case where your video doesn’t have to be professional quality– you’re probably the only one who is going to look at it. But any kind of recording can help make you aware of issues with your performance that you might not have otherwise realized.
Do you look like you’re trapped behind the lectern? Are you clearly afraid? Is your posture bad? Do you fidget or repeatedly touch your nose while you’re speaking? These are just a few of the bad habits that speakers can have but remain totally unaware of until they actually see themselves speaking. So record yourself and review the result with a critical eye so you can make a conscious effort to eliminate any issues you may find.