It is sad to see someone trying to cast out a demon and asking the demon, "Do you know who I am?" or shouting loudly trying to make the demon submit. They don't realise it is not their power that can cast out demons but the authority of Jesus in His name. It is not of us (2Co.4:7 KJV). This gives us boldness, because it is not about how godly we are, how much we know the Bible, etc. It's about the fact that Jesus has overcome the Devil and all demons, and disarmed them of their power when He died and rose up (Co.2:15). If we belong to Him, He has granted us the authority to cast out demons (Lk.10:19). The sons of Sceva tried to use a formula "In the name of Jesus" without knowing Him (Ac.19:13).
But it is not only with respect to demons that we need to remember this, that power belongs to God (Ps.62:11) and that He will not give His glory to another (Is.48:11). In whatever we do, if we can remember this, we can subject ourselves to Him and depend on Him as wholly as possible. For example, in preaching or doing any other ministry, if we are conscious of the fact that it is not we who can bless others but God, we will learn not to depend on our cleverness or skills but on His anointing that alone can bring about lasting results.
When Joshua was going to take Jericho, the first city in the Promised Land, he listened to God and His instructions. But after that great success, he thought he knew how to handle things by himself at Ai, the next city, and failed miserably. Isn't that our tendency too? A little bit of success and it goes to our head. We begin to think we have done it! And our pride goes before a fall!
The apostle Paul knew what a dangerous position he was in, where he could easily trust in himself because of his cleverness, knowledge, heritage, training, etc. So he took extra care not to project himself or his oratorical skills when he shared the Gospel with the Corinthians (1Co.2:3-5). He wasn't trying to impress them but to bless them with the pure truth of God which alone could save them. Otherwise, they could have been left with the impression, "What a great speaker!" and missed the penetrating power of the Holy Spirit.
Relying on the power of the Holy Spirit to work through us is one of the powerful secrets of ministry. We can do this only when we know how impotent and helpless we are without Him, whatever theatrical skills or special effects we employ. Waiting on Him to speak the word that He gives, and speaking in the way He wants, we can seek to leave the people thinking about the message they heard rather than the greatness of the messenger. Whether we plant or water, it is only God who can give growth (1Co.3:6,7).
If we truly know who the Lord is and our position before Him, our highest goal will be to ensure that He receives the glory that is due to Him (Ro.11:36). We will seek avoid getting into the limelight, and if it comes to us we will be quick to pass on the glory to Him openly or in our heart.