Preaching isn't a rehearsal of historical facts. It's not the dissemination of information. It is not talking, sloganeering, cheerleading, or even speechifying. It is the bearing witness of God's righteousness revealed in Christ Jesus. And God somehow inhabits that witness bearing. Remember the disciples on the road to Emmaus? After Jesus had opened up the Word to them, they said, "Didn't our hearts burn within us?" Or remember when Peter was preaching at Cornelius's house? Luke tells us "the Holy Spirit fell on all those listening to the Word." Where else besides Bible preaching do you see that kind of thing happening?
Writing to the Christians in Thessalonica, Paul makes it clear that Gospel preaching is brimming with the very power of God.
For we know, brothers, beloved by God, that he has chosen you, because our message of the gospel came to you not in Word only, but also in power and in the Holy Spirit and with full conviction just as you know what kind of persons we proved to be among you for your sake. (1 Thess. 4–5)
The thing is, the Thessalonians didn't receive Paul's message as the word of a turncoat Pharisee with a troubled history of trying to destroy the church. They received it as the very word of God.
We also constantly give thanks to God for this, that when you received the word of God that you heard from us, you accepted it not as a word of men but what it truly is, God's word, which is also at work in you believers. (1 Thess 2:13)
While there is power in preaching, it must be mixed with faith. Otherwise, even the word of God will be rendered ineffectual. Just ask those Nazarenes. (Mark 6:5, 6)
Kenneth Hagin was one preacher who had a particularly strong anointing resting on him. Watch the video below at the 57:00 to 1:07:00 marks to see the effects of preaching in the power of the Spirit.