Letter 916: Libanius explains that his speech on the law was not an exercise but a political defense of public speaking.

I now grant that the speech about the law was well done, since that is what you both say and write about it. It was not written after the repeal of the law forbidding public speaking merely as an exercise. It was written for this very fight: that those who are able to speak should always be allowed to speak. That was the purpose that produced the speech. At home, though, it was held back, because people familiar with palace affairs persuaded us that this was safer. The fear was that some people might stir up the author of the law against the author of the speech. But Fortune took my place. The same voice both made the law and abolished it, and so the speech came into the theater, and its exhortation could take the form of praise. You, for your part, do well to give yourself no more to the gardens so near you than to speeches. Your present letter both said this to me and made it clear.