Jesus said we would receive power after that the Holy Ghost is come upon us. (Acts 1:8)

The Holy Ghost is a promise to us when we repent and are baptized in the name of Jesus.

"Then Peter said unto them, Repent, and be baptized every one of you in the name of Jesus Christ for the remission of sins, and ye shall receive the gift of the Holy Ghost." - Acts 2:38

The Holy Ghost – the Spirit of Jesus in us – is powerful!

When the lame man that sat at the temple gate was healed in the name of Jesus, Peter preached to the people, as they greatly wondered at the miracle.

Peter preached the gospel - the death, burial, and resurrection - and the name of Jesus.

"And his name through faith in his name hath made this man strong, whom ye see and know: yea, the faith which is by him hath given him this perfect soundness in the presence of you all." - Acts 3:16

The priests, and the captain of the temple, and the Sadducees, being grieved that they taught the people and preached through Jesus the resurrection from the dead, laid hold on Peter and John and put them in jail until the next day.

About five thousand believed after hearing Peter preach!

"Howbeit many of them which heard the word believed; and the number of the men was about five thousand." - Acts 4:4

The next day they were released from jail and brought before their rulers, and elders, and scribes, and Annas the high priest, and Caiaphas, and John, and Alexander, and as many as were of the kindred of the high priest.

"And when they had set them in the midst, they asked, By what power, or by what name, have ye done this?" - Acts 4:7

Then Peter, filled with the Holy Ghost, said unto them,

"Be it known unto you all, and to all the people of Israel, that by the name of Jesus Christ of Nazareth, whom ye crucified, whom God raised from the dead, even by him doth this man stand here before you whole. This is the stone which was set at nought of you builders, which is become the head of the corner." - Acts 4:10-11

"Neither is there salvation in any other: for there is none other name under heaven given among men, whereby we must be saved." - Acts 4:12

The council then conferred. They wanted to stop the preaching of the name of Jesus!

"But that it spread no further among the people, let us straitly threaten them, that they speak henceforth to no man in this name. And they called them, and commanded them not to speak at all nor teach in the name of Jesus." - Acts 4:17-18

After further threatening them, they let them go. And they returned to the other believers, and reported all that the chief priests and elders had said unto them.

When they heard the report, all the believers lifted their voices together in prayer to God.

"And when they had prayed, the place was shaken where they were assembled together; and they were all filled with the Holy Ghost, and they spake the word of God with boldness." - Acts 4:31

There was power, so much so that the place was shaken where they were praying!

With this power came boldness to speak the word of God and the name of Jesus.

"And with great power gave the apostles witness of the resurrection of the Lord Jesus: and great grace was upon them all." - Acts 4:33

GREAT power was upon them after they prayed and were filled with the Holy Ghost – power to be witnesses for Jesus.

"But ye shall receive power, after that the Holy Ghost is come upon you: and ye shall be witnesses unto me both in Jerusalem, and in all Judaea, and in Samaria, and unto the uttermost part of the earth." - Acts 1:8