Why were Paul's Missionary Journeys so important?

The importance of Paul's 'missionary journeys' must be established from Acts of the Apostles since, as Raymond E. Brown (An Introduction to the New Testament) says, the three journeys are only a convenient classification developed by students of Acts. In his undisputed letters Paul gives us no information about the first missionary journey, and Acts actually seems to contradict Paul's own account of his itinerary. Even the subsequent journeys in Acts seem problematic when compared with Paul's epistles, although some scholars see scope for them to have been historical. Given their absence from Paul's own account, and without confirmation from any other source, the three missionary journeys of Acts can not be considered historically important.

From a theological perspective, the journey to Cyprus was important, because it demonstrated Paul's extraordinary ability to perform the miracle of harming Elymas (bar-Jesus) by depriving him of his sight for a season. Paul himself had never mentioned the journey to Cyprus and never claimed to be capable of performing miracles. From the epistles alone it seems that Paul had not sought to cause others any harm in the course of his mission.