“Homiletics,” is the word used to indicate the science, the skill, or the art of preparing sermons and the preaching of them.
In order for a discourse to be properly prepared and delivered three things are of the utmost importance…

a. The content of the sermon. This has regard to its message that is to be preached.

b. The construction of the sermon. This largely concerns its mechanics - the essential parts of it, and the putting together of it. 

c. The communication of the sermon which has to do with the manner of the preaching of it to the people who are listening. This will largely focus on the proper use of our voices.