But though we had already suffered and been shamefully treated at Philippi, as you know, we had boldness in our God to declare to you the gospel of God in the midst of much conflict. (1 Thessalonians 2:2 -- ESV)
Paul is going to defend the arrival of the Gospel message in Thessalonika, but he is going to do this by pointing to his own arrival. Don't confuse this for prideful boasting, his goal is to make sure that they know that he is different from other traveling philosophers that the Thessalonicans would have been very familiar with. He starts this differentiation by pointing out the suffering that they experienced in Philippi (Acts 16:22-24). He also points out that the declaration of the gospel, though in the middle of conflict, was still done with boldness. If nothing else, this tells you that popularity is not Paul's main concern.