Nothing is more important to the preacher, or to any Christian, than the Holy Spirit. He is "God with us". The Spirit empowers us to live godly lives full of love, joy, peace, patience, kindness, goodness, faithfulness, gentleness and self-control. The Spirit sets us free from our slavery to sin. He reminds us of the words of Jesus, and helps us to walk humbly and obediently with the Triune God.
For preachers, the Spirit empowers us when we study and when we preach. He is with us through the whole process of sermon preparation. Some people have this understanding of the Spirit that he doesn't show up until church starts. That's ridiculous. He is with us, always. And he wants to be included in everything we do, especially when it relates to God's word.
Do you pray when you sit down to study the Scriptures? Do you invite the Spirit to guide you as you do you exegesis? Do you ask him to lead you as you let ideas ruminate in your mind, or write them down on paper, or type them into the computer? Do you surrender your words, and your agenda, to the Spirit of God, praying that you would have the strength to take up his words and his agenda?
There have been times when I've done a lot of work on a sermon, even typed several pages of it, but then I got a sense that it wasn't right. It wasn't what the Spirit wanted to communicate to the church. There have even been times when I've tossed the whole sermon out as I was walking up to the pulpit. That's always interesting. While that sort of thing is fine to do from time to time, I don't want to live in that place. I want to make sure I'm actively and intentionally inviting the Holy Spirit into the sermon process from the very beginning. Preaching without the presence and power of the Holy Spirit is nothing more than public communication.