What is the purpose of the justification step in an extemporaneous speech?

The purpose of the step of justification in an extemporaneous speech is that it captures the attention of the listeners, and presents the theme of the speech, this may last a little more than a minute, has the objective of capturing public attention, speaking about the background of the speech theme to generate reliability in what it is going to be said and at the same time it explains why the speech is important and how it is going to be structured.

It is involved in catching the attention of the spectators and adding theme into the speech.  

Explanation:

It would be taking place for less than a minute. Its main aim is falling into the public attention to capture with. It is related in adding theme over the side of the background in order to generate reliable results.

The answer is telescope.