Training, practice, rehearsal, run-through, whatever you call it personally it’s needed.
It’s key to any public performance, particularly important with speeches designed to promote a point of view, support an argument or simply to convey your sincerity about a subject. Many speakers feel they are practiced enough, have enough experience maybe even believe they are at the top of their game. They aren’t, I’m not and you won’t always be.
I spent several years working in radio and even before reading out a simple weather report whilst the news was on or a song was being played I would read the weather report out loud to myself. Not in my head, “out loud” it was the only way I could ensure I would be able to pronounce all the words, read it slow enough to be understood and with enough vocal brightness to stop it being simply a weather report.
Try reading this aloud without any errors: