There is a substantial difference between being filled with the Holy Spirit and not being filled. The apostle Peter went through a period of stumbling, defeat and insecurity. But Jesus had promised the disciples they would receive power when the Holy Spirit came on them, and they would be His witnesses.
Peter lived that experience in the upper room where it says: "And suddenly there came a sound from heaven, as of a rushing mighty wind, and it filled the whole house where they were sitting. Then there appeared to them divided tongues, as of fire, and one sat upon each of them. And they were all filled with the Holy Spirit and began to speak with other tongues, as the Spirit gave them utterance" (Acts 2:2-4, NKJV).
For three years, Peter walked with Jesus and saw the most glorious moments of the Lord's ministry. But when Peter had to make a stand for Christ, he refused to do so. In the upper room, when he received the fulfillment of Christ's promise, the fullness of the Holy Spirit enabled him to become a faithful witness.
We do not change because we witness miracles and wonders, nor do we change because we attend a beautiful worship service. Only an upper room experience can transform us--a personal experience with Christ through His Holy Spirit.