There's a good post about the difficulties of preaching over at Shored Fragments.
He makes a solid point - it is pretty tough to have something worthwhile to say on a weekly basis to the same group of people. We don't expect that of many other professions. Most professional speakers and experts repeat the same message to different people even if they speak weekly. Broadcasters who speak a lot, and sometimes to the same audience, do it with a team of researchers and writers at their disposal. A minister is usually on their own. Grab a Bible, sit at your keyboard, write something poignant - go. Now do it again and again and again.
So, yeah, I agree: preaching is hard.
And it is also easy.
It is easy because we don't have to preach an entirely new message every week. We preach the same message in a slightly different way. What is required is a facility with language and metaphor, not a bottomless supply of new ideas and information.
It is easy because sermons grow organically out of your life together in the church. I don't have to pull a sermon out of thin air, I talk about what naturally arises in the course of daily life.
It is easy because we are not held to an absurd standard of polish and rhetorical brilliance. Not every sermon has to be a masterpiece. If you kill yourself over every syllable it will be forgotten just as quickly as if you improvise the entire thing. Being faithful to your purpose in preaching is more important than any amount of technical mastery.
It is easy because there are straightforward techniques one can practice and master with time. Writing is not a mysterious artform. Public speaking is even less mysterious. Practice elocution, pith, and delivery. You will get better.