THE GOSPEL IS OLD, NOT NEW (ACTS 17:2-4). Paul went into the synagogue, and on three Sabbath days he reasoned with them from the Scriptures, explaining and proving that the Messiah had to suffer and rise from the dead. Paul reasoned that the Gospel was not something new, but old. Later, he would write to the Romans:
Paul, a servant of Christ Jesus, called to be an apostle and set apart for the gospel of God—the gospel he promised beforehand through his prophets in the Holy Scriptures regarding his Son, who as to his human nature was a descendant of David, and who through the Spirit of holiness was declared with power to be the Son of God, by his resurrection from the dead: Jesus Christ our Lord (Romans 1:1-4).
The Gospel was conceived in eternity past and gradually unfolded in the OT Scriptures. Throughout his ministry, Paul used numerous OT quotes and illustrations to demonstrate this truth. Neither Christ nor Christianity burst on the scene unexpectedly, both were planned and predicted by the prophets in the Holy Scriptures. When he summarized the Gospel, he also said it was old, not new:
For what I received I passed on to you as of first importance: that Christ died for our sins according to the Scriptures, that he was buried, that he was raised on the third day according to the Scriptures, and that he appeared to Peter, and then to the Twelve (1 Corinthians 15:3-5).
Some Jews were persuaded but the great number responding positively to the Gospel were God-fearing Greeks and prominent women.