Authority of a God's servant

While they were worshiping the Lord and fasting, the Holy Spirit said, “Set apart for me Barnabas and Saul for the work to which I have called them.”
When they arrived at Salamis, they proclaimed the word of God in the Jewish synagogues. John was with them as their helper.
Sergius Paulus, the proconsul, an intelligent man,  he wanted to hear the word of God. But Elymas the sorcerer opposed and tried to turn the proconsul from the faith.
Paul, filled with the Holy Spirit, looked straight at Elymas and said,  “You are a child of the devil and an enemy of everything that is right! You are full of all kinds of deceit and trickery.
From Paphos, Paul and his companions sailed to Perga in Pamphylia, where John left them to return to Jerusalem.
The church at Antioch, directed by the Holy Sprit,selects its best men for pioneer work.
Saul adopts the Roman version of his own name: Paul. From now on it is 'Paul and company', as he takes the lead.
Why?
1.Holy Spirit says while they are worshiping the Lord and fasting.
2.Preaching gospel is proclaim the word of God.
3.God's servant, Christian, has authority to defeat the devil and an enemy of everything that right.
4. There is weak brother accompany us in work for the Lord.
How?
Christian has the authority from the Lord to conquer the evil one.