vs. 4 Every Sabbath he reasoned in the synagogue, trying to persuade Jews and Greeks.  vs. 19.  They arrived at Ephesus, where Paul left Priscilla and Aquila.  He himself went into the synagogue and reasoned with the Jews.  vs. 24.  Meanwhile a Jew named Apollos, a native of Alexandria came to Ephesus.  He was a learned man, with a thorough knowledge of the Scriptures.  vs. 28.  For he vigorously refuted the Jews in public debate, proving from the Scriptures that Jesus was the Christ.

Today, when we use the word Scripture we are speaking of the entire Bible.  These folks did not have the New Testament because they were living it, so they were proving Jesus was the Messiah using only the Old Testament, the fact of Jesus’ resurrection and  His crucifixion.  No one, then, today, Jew or Gentile,  has any excuse because the plan of salvation through a sinless Saviour is clearly presented in the Old Testament and the New.