Question

Is the only way to give a professional speech is to stand behind a lectern

Answer 1

Absolutely not.

There are many ways to give a professional speech, and not necessarily behind a lectern. Professionals speak ( some more than others). Lawyers use verbal communication in a jury, defending a case and they are not behind a lectern. Medical advice is given too in a class, at university. In fact, politicians give professional speeches everywhere, when they open up a new facility, or at campaigns.

Professionals contribute specialized, technical knowledge to which  citizens would not otherwise have access, and they study oratory techiques to make speeches better.