Many public speakers equate the speech conclusion merely as a summary of their presentation. To a small degree, it is that.
To any speaker who has gained any credibility however, they understand a fundamental truth in public speaking:
If the audience leaves your presentation without any shift in perspective, thoughts or behaviour, you've wasted their time as well as your own.
So, let's begin with the basics. Yes, summarize the content of the body of your speech (another key reason why you want to keep your main presentation at 2 - 3 points, it's much easier to summarize than, say, 17).
Also, the conclusion must somehow link to the speech opening. It could be by readdressing the same first lines or facts verbatim, or it could reveal an answer to a question put forth at the start, or it could be ways that are much more subtle.
What is essential in your conclusion, however, is that the speech purpose corresponds exactly to your speech opening. Mixing up your purposes as bookends will confuse and potentially frustrate your listeners. Help them repackage what you presented to them in a way that is neat and tidy.
That's expected in any presentation.
The challenge of a great public speaker is to leave the audience with a message they can take home that will affect them. Will cause something to stir within them, motivate them, allow them to see things with new eyes.
That's where the true value of a speech is. It's what the audience takes home within them.
Great speakers set up "pings" throughout the body of their speech. At the end of their presentation they draw all these threads together to a single point of focus, incorporating it into their speech conclusion. This is the added value that sets apart a memorable speech.