Acts 2:4-6, 36-38, 41, Acts 5:42
Jesus said that when the Holy Spirit comes upon us, we will proclaim Jesus Christ to the whole world. (Acts 1:8)
Acts 1:8 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.
The Holy Spirit came upon the disciples in Mark's upper room. (Acts 2:4-6)
Acts 2:4 And they were all filled with the Holy Ghost, and began to speak with other tongues, as the Spirit gave them utterance. 5 And there were dwelling at Jerusalem Jews, devout men, out of every nation under heaven. 6 Now when this was noised abroad, the multitude came together, and were confounded, because that every man heard them speak in his own language.
When the Holy Spirit came on Peter, he preached the gospel that Jesus was the Christ. So many people came to believe it. (Acts 2:36-38,41)
Acts 2:36 Therefore let all the house of Israel know assuredly, that God hath made the same Jesus, whom ye have crucified, both Lord and Christ. 37 Now when they heard this, they were pricked in their heart, and said unto Peter and to the rest of the apostles, Men and brethren, what shall we do? 38 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. 41 Then they that gladly received his word were baptized: and the same day there were added unto them about three thousand souls.
And the disciples taught and preached that Jesus was the Christ every day. (Acts 5:42)
Acts 5:42 And daily in the temple, and in every house, they ceased not to teach and preach Jesus Christ.