In Acts it is written that St. Paul, while living in Jerusalem, spoke boldly in the name of the Lord Jesus and disputed with the Hellenists, that is, with Jews who lived among the nations and happened to be in Jerusalem at that time. They were stirred up against him and sought to kill him.
This compelled him to withdraw from Jerusalem, and the believers escorted him for safety to Caesarea, from where he went to Tarsus, his birthplace (see Acts 9:29-30). The road lay through Syria.
Perhaps St. Paul only crossed Syria at that time, but in Cilicia he surely preached. It was hard for him to restrain himself from proclaiming in his birthplace the Gospel that filled his heart with inexhaustible joy over salvation.
That he truly preached there and even founded churches can be concluded from the fact that later, during his second journey, he passed through Syria and Cilicia strengthening the churches (see Acts 15:41). How would he have strengthened them if he had not first planted them?
Therefore St. Chrysostom writes: "After meeting Peter, he again begins the word of preaching and the struggle set before him, not touching the Jews, both because he was sent to the nations and because he did not wish to build on another's foundation."
Jerome says the same: "He went to Cilicia, wishing to draw it to faith in Christ, preaching to it the call to repentance."