I love it when the Holy Spirit shows up in worship. Just this week, He showed up in a really special and unique way, and He "invited" me to ditch the sermon I'd planned and go in a different direction. It was exciting and made me think a lot.
One enticing thought was "wouldn't it be great to do this all the time?" Meaning - if the Holy Spirit wants to speak spontaneously through me, couldn't I spend my time during the week differently? Think of all the time I usually spend studying and writing a sermon that could be freed up to do other things!
But I don't believe for a minute that the Holy Spirit plans to work like that all the time. In fact, the Holy Spirit most often "shows up" through the study time and reflection time and prayer time that I regularly put into the week's sermon.
There are times when people have mentioned to me, "You must have been in our house this week, because you spoke exactly to the situation that's been going on." - whenever that happens, it's because the Holy Spirit has directed me to write that part of the sermon directly to you. (as an aside, every time I've written a point in a sermon directly to one person, that person just never seems to show up that Sunday - or that person shows up and has no idea that I'm talking to them. And that's a good thing, because when I do that, it's by *my own* authority, and really, I don't have any authority on my own; it's God's authority, and I'd prefer to let Him speak)
There are some people who believe that He only shows up spontaneously, but how limiting is that to GOD? Seriously, do you believe God can speak through me on Sunday morning if I throw out my manuscript, but you don't believe He will speak through me if I'm spending my time in prayer, Bible study, and reflection? That's awfully limiting of the God of the Universe!
And our God is not a God of chaos, but a God of order. That's why I take as long as I do preparing a sermon.