Being passionate about a topic is a great place to start when it comes to delivering inspirational speeches. However, just because you have passion for it does not guarantee the speech will be inspirational.
You must be able to satisfy 3 needs simultaneously in order for the audience to feel ignited with the same passion that you hold.
First, your audience must get the direct impression that you are one of them. They need to know that you have felt the exact same fears, concerns, trepidation that they are experiencing right now as they listen to you.
You have to show that you are familiar with the same trenches that they are struggling through right now. Very few people take any direction from someone who hasn't been in their shoes.
Secondly, you have to be able to show, without the slightest doubt, that you are credible. That you have reached the promised land, or very well near, as to what you are preaching.
Imagine a speaker attempting to inspire you to go out and climb K2, when it's quite clear by looking a him that he hasn't even gone on a hike in years, let alone conquered that mountain. How effective would he be?
And, finally, you must be able to bridge that gap to your listeners. This bridging is only meaningful when it is definitive. Theories are weak and ineffective. You must give your audience solid, tangible steps, right in the now, in order to gain their confidence.
For instance, for an inspirational speech on self-confidence, you might introduce a list of things your audience already did today that were small, yet significant steps towards self-confidence already. Perhaps you list 6 things that each of them did by the time they got there.
Well, now they've all done 6, surely they can all do 1 or 2 more. Make it actionable. Right here, right now, as another concrete measure to symbolize another benchmark. Another success they can build on when it comes to increasing their confidence. Each step is pivotal.
In essence, to give a commanding inspirational speech, you have to be 3 people rolled into 1.