I once heard John Piper say in an interview, "Self-consciousness is the curse of the preacher." The context of the conversation was concerning the infamous "gesturing" of Piper in the pulpit. He made clear that he does not practice, plan, or otherwise pay attention to that stuff. Furthermore, it would be deadly if he did.
By self-awareness I mean the unhealthy fixation of the preacher upon himself. When the preacher is thinking about himself before he is preaching, when he is preaching, and after he is preaching, then he is dangerously self-aware.
And why would it be a danger for the preacher?
1. It could divert his focus.
The task of the preacher is to communicate God's Word in such a way that his hearers will be captivated with the greatness of God. To this end the preacher must be focused on God. He must be enveloped in the majesty of God and speak as one who is personally impressed with him.
If the pastor spends his time trying hit the perfect inflection, making the right gesture, telling the right kind of story, or making the perfect face, then he is distracted. I have heard of some men who weekly watch videos of their sermons to improve. Doubtless some of this study can be helpful. But if you are breaking down your motions with the detail of an NFL commentator, then your focus may be off.
2. It may detract from God's power.
The logic goes something like this: If we could just improve our craft a bit then perhaps they will trust and treasure Christ. But conversion and growth does not work this way. God has chosen to use the weak things—like imperfect people preaching—to show his power (cf. 1 Cor. 1:18-31). In this weakness God shows himself powerful.
So by all means, try to remove needless distractions. However, do not seek to make the message more powerful by putting some air in the gospel sails. You can't do it. It will inevitably deviate from God's plan and detract from his power.
3. It may lead to pragmatism and manipulation.
I have often wondered how some preachers started doing certain things while preaching. Some guys wear outlandish clothing, say shocking things, and even deploy props on stage during their sermons. How does this happen? Nobody just wakes up on a Sunday morning and says, "I think I'll ride my motorcycle to the pulpit today." People don't jump to pragmatism overnight.
I believe they really want to be effective. You can see how this type of thing could dangerously progress. The preacher's unhealthy fixation upon himself can lead him down unexpected roads.
We know that manipulation has always been a pulpit felony. If the preacher is manufacturing emotion in himself or his hearers only to get a response (however "good" his end-goal) he must repent. Preachers, of all people, must not manipulate people. We proclaim truth!
But we have renounced disgraceful, underhanded ways. We refuse to practice cunning or to tamper with God's word, but by the open statement of the truth we would commend ourselves to everyone's conscience in the sight of God. (2 Cor. 4:2 )
4. It may be quenching the Holy Spirit.
Another way preachers could be too self-aware is to try to defuse emotion in the pulpit. Some guys are greatly moved with emotion, even to tears, while preaching. There's nothing wrong with this response. However, in his unhealthy fixation upon himself the preacher may try to resist this emotion. But if he is genuinely moved by God the Holy Spirit, how can he suppress being moved? Isn't this hypocritical?
Think about it: we preach and pray for "God to work in people's lives" only to resist him in our own? What an insult to the Trinity for me to mitigate the divine passion for his glory and honor by trying to preserve and promote my own! Being too aware of self could lead to a lack of awareness of the Holy Spirit.
When a preacher fixates on himself, his preaching becomes a personal performance rather than proclamation of God's Word. And the preacher can never let himself become the spectacle. He cannot be the show. He gets out of the way by being wrapped up in and carried away in the God he proclaims. I think this is what God the Holy Spirit is doing when he uses the preacher's personality and expressiveness to serve the Word of God. As Piper teaches:
You want the significance of what you are saying to be seen and felt, and I suppose it is largely a personality thing as to how much expressiveness you give with your voice and how much expressiveness you give with you body. But for me, it is just who I am and what I do and it is part, it is just part of a language.
Be yourself and don't be too conscious of yourself. Just preach the Word of God.