What makes a person a convincing public speaker?

Just today, I was told “you cant be very educated tho caus ur an atheist i mean hava a look around man watch loi giglio man open your eyes….....no offence.”

This has got me to thinking, what makes a person able to present a speech with rubbish content, but still able to convince thousands of others to the point where they use this content to try and prove others wrong? Is it because the audience already shares these views, or is there a hidden secret to their eloquence? There are plenty of Christian apologists out there who present far more intellectually convincing cases, so what is special about Louie Giglio and others of that breed who do not present a solid argument? Is it limited to religious spheres, or could someone do the same for conspiracy theories etc.?