Learning to be filled (controlled and empowered) with the Holy Spirit is the most important discovery of the Christian life. You can experience the abundant life Jesus promised! You can introduce others to Christ!
Even though they had been with the Lord for three years of His earthly ministry, the apostles were not equipped to carry out our Lord's Great Commission until they were filled with the Holy Spirit.
Jesus also promised that we would do greater works than He did. Obviously we cannot accomplish these greater works through our own self efforts. They will result from the Son of Man, who came to seek and save the lost, working through us in the power of the Holy Spirit. Our responsibility is to follow Christ; His responsibility is to make us fishers of men.
The Holy Spirit whom the disciples received at Pentecost enabled them to change the course of history. That same Holy Spirit is available to every believer today.
Tragically, multitudes of Christians do not know how to be filled with the Spirit. Consequently, they go through life without ever experiencing the abundant and fruitful life which Christ promised to all who trust and obey Him.