1 Thessalonians 2:14

For ye, brethren, became imitators of the churches of God which are in Judea in Christ Jesus: for ye also suffered the same things of your own countrymen, even as they did of the Jews;

It was Jewish persecution which first broke against the infant church; and it was conspicuously against their own countrymen; here Paul compared the persecutions of the Thessalonians which they had endured at the hands of their Gentile countrymen to that of the Jewish-Christians in Judea, noting that both had bravely and courageously endured. However, as a glance at Acts 17:13 will show, the Jews were those who had instigated and promoted the persecution in Thessalonica, even though the details of it were executed by Gentiles. The very thought of such a thing seems to have triggered in Paul's mind the startling words written next. Kelcy said that for denunciative bitterness, "This is unparalleled in any of Paul's other writings."[25] However, it should not be thought that Paul was in any manner reprehensible in the denunciation that followed. He said nothing that Christ had not said; all that he said was true; and all that he said needed to be said.