Answer:
1- Your answer is in the paragraph itself. Those who choose violence might inflict physical pain and can deal a lot of damage, but there's a limit. There's only so much damage one can do before getting tired or giving up. Words on the other hand are powerful, and have no limit. You can reach so many more people around the world, and cand e timeless as we have the internet now as well.
2- Persuasion here is being referred to as an art rather than science because of the words that you put together and sentences that you form that can change someone's mind. Changing one or two words can change the whole outlook of a sentence.
3- This one is talking about how words, or persuasion over a matter or discussion, over force or violence, will lead to a more successful and civilized society. There will be a lot of differences between people, especially in a society, so being rational and sorting things out with words will keep everyone pleased.