Like others who teach or write about preaching, I have noted before (such as here, here, or here) that often people confuse teaching or lecturing with preaching. Preaching certainly includes teaching but goes beyond it in such things as the singular purpose and moral force it is to have.
Martyn Lloyd-Jones in Preaching and Preachers spoke to this subject. He said, "There are men who think they are preaching the Gospel when actually in fact they are simply saying things about the Gospel." He warned that knowledgeable men could simply be lecturing rather than preaching. Lloyd-Jones even stressed this further by going so far as to say,
Here I believe that we have to draw a distinction between two elements in preaching. There is first of all the sermon or the message – the content of that which is being delivered. But secondly, there is the act of preaching, the delivery if you like, or what is commonly called ‘preaching.’ It is a great pity that this word ‘preaching’ is not confined to this second aspect which we may describe as the art of delivering the message.
What the good doctor and others are stressing is that we must distinguish between what a preacher learns in the study of God's Word and what he brings to the pulpit for God's people. Though clearly related, with the latter dependent on the former, they are not the same. As one who coaches young men in their preaching, I regularly remind them to discern between sermon preparation and sermon proclamation. For there is a necessary distinction to be made between the content of a message and the delivery of it.
Herein lies the difference between hermeneutics and homiletics. Hermeneutics by definition is “the science of interpretation.” From the Greek word "hermeneuo" meaning "to interpret" or "to translate," hermeneutics defines the principles by which we understand a text or even the spoken word. Biblical hermeneutics has some additional rules added as the text is the sacred Word of God.
Homiletics is also from the Greek, from the word "homiletikos" which means “conversation” and has the sense of a discourse on a moral theme. Homiletics is the application of the general principles of rhetoric to the specific department of public speaking. As Christian preaching is based on God's Word, historically preaching has been thought of as sacred rhetoric.
Thus, hermeneutics supplies the understanding for the sermon, whereas homiletics is the actual preaching of the sermon. This distinction ties into the point Lloyd-Jones was making in the quote above. To help my students understand this distinction, I give them analogies like the following.
Hermeneutics is the building material & construction; homiletics is the building walked into.
Hermeneutics is the ingredients & the cooking: homiletics is the baked bread served.
Hermeneutics is the car’s body & engine parts in assembly; homiletics is the race car driven fast.
Hermeneutics is sharpening the arrow and tightening the bow; homiletics is drawing the bow back and letting the arrow fly straight and true.
Hermeneutics is buying the ammo and cleaning the gun; homiletics is shooting the deer.
Indeed, hermeneutics is discovering the clear sense in your mind and heart of a text and its theme, whereas homiletics is driving home that theme with conviction to the hearts of others.