"And my speech and my preaching was not with enticing words of man's wisdom, but in demonstration of the Spirit and of power." 1 Corinthians 2:4
If in preaching the Gospel you substitute your clear knowledge of the way of salvation for confidence in the power of the Gospel, you hinder people getting to Reality. You have to see that while you proclaim your knowledge of the way of salvation, you yourself are rooted and grounded in faith in God. Never rely on the clearness of your exposition, but as you give your exposition see that you are relying on the Holy Spirit. Rely on the certainty of God's redemptive power, and He will create His own life in souls.
When once you are rooted in Reality, nothing can shake you. If your faith is in experiences, any thing that happens is likely to upset that faith; but nothing can ever upset God or the almighty Reality of Redemption; base your faith on that, and you are as eternally secure as God. When once you get into personal contact with Jesus Christ, you will never be moved again. That is the meaning of sanctification. God puts His disapproval on human experience when we begin to adhere to the conception that sanctification is merely an experience, and forget that sanctification itself has to be sanctified (see John 17:19). I have deliberately to give my sanctified life to God for His service, so that He can use me as His hands and His feet.