Wise advice on planning

A speech without a plan is a journey without a map - Dale Carnegie
At its core, this quote means that winging it is a losing strategy. Without a clear structure, your message will meander and fail to land with impact.

What purpose means

A definite purpose is the soul of a speech - Dale Carnegie
At its core, this means that without a clear, singular goal, a speech is just a hollow shell of words. The "soul" is the animating force, the thing that gives it life and makes it matter.