The word “strengthen” (episterizo) is a present tense verb which means that the action to make stronger or support is an ongoing function. This is pictured by placing a stake next to a young plant until it grows and matures (see picture below). This meaning is further emphasized by Luke’s use of the words “encouraging them” (parakaleo), meaning “call to one’s side, or summon together for a purpose”. It is evident that these two ideas are intended to work together as disciples are gathered for the purpose of having their faith made stronger and more mature.
Though Paul and Barnabas did not spend a lot of time in any one of these places, the intensity of their visit combined with “committing them to the Lord” served to bind the new believers to the words of truth and the Head of the church, Christ. This principle is essential, not just for new church plants, but also for any church that is weak in the faith. This does not require any title for someone to fulfill. It only needs your heart ignited by the Holy Spirit to live out this principle.