Acts 11:26, Acts 17:1-3, Acts 18:5, Acts 19:8-10, Acts 20:20-21, Acts 28:23, 30-31 After meeting the resurrected Jesus on the road to Damascus, Paul realized that Jesus was the Christ. So he preached throughout his life that the Christ prophesied in the Old Testament was Jesus.
Acts 9:19 And when he had received meat, he was strengthened. Then was Saul certain days with the disciples which were at Damascus. 20 And straightway he preached Christ in the synagogues, that he is the Son of God. 21 But all that heard him were amazed, and said; Is not this he that destroyed them which called on this name in Jerusalem, and came hither for that intent, that he might bring them bound unto the chief priests? 22 But Saul increased the more in strength, and confounded the Jews which dwelt at Damascus, proving that this is very Christ.
Acts 17:1 Now when they had passed through Amphipolis and Apollonia, they came to Thessalonica, where was a synagogue of the Jews: 2 And Paul, as his manner was, went in unto them, and three sabbath days reasoned with them out of the scriptures, 3 Opening and alleging, that Christ must needs have suffered, and risen again from the dead; and that this Jesus, whom I preach unto you, is Christ.
Acts 18:5 And when Silas and Timotheus were come from Macedonia, Paul was pressed in the spirit, and testified to the Jews that Jesus was Christ.
Acts 19:8 And he went into the synagogue, and spake boldly for the space of three months, disputing and persuading the things concerning the kingdom of God. 9 But when divers were hardened, and believed not, but spake evil of that way before the multitude, he departed from them, and separated the disciples, disputing daily in the school of one Tyrannus. 10 And this continued by the space of two years; so that all they which dwelt in Asia heard the word of the Lord Jesus, both Jews and Greeks.
Acts 20:20 And how I kept back nothing that was profitable unto you, but have shewed you, and have taught you publicly, and from house to house, 21 Testifying both to the Jews, and also to the Greeks, repentance toward God, and faith toward our Lord Jesus Christ.
Acts 28:23 And when they had appointed him a day, there came many to him into his lodging; to whom he expounded and testified the kingdom of God, persuading them concerning Jesus, both out of the law of Moses, and out of the prophets, from morning till evening. 30 And Paul dwelt two whole years in his own hired house, and received all that came in unto him, 31 Preaching the kingdom of God, and teaching those things which concern the Lord Jesus Christ, with all confidence, no man forbidding him.
And the disciples who heard the gospel from Paul also preached that Jesus was the Christ. So they earned the nickname Christians by others. (Acts 11:26)
Acts 11:26 And when he had found him, he brought him unto Antioch. And it came to pass, that a whole year they assembled themselves with the church, and taught much people. And the disciples were called Christians first in Antioch.