The Greek episterizo (Strong's G1991) means 'to strengthen,' 'to support,' or 'to establish.' It combines epi (intensive) and sterizo (to fix firmly, establish, support). This word appears four times in Acts, all in the context of Paul and Barnabas returning to already-planted churches to strengthen and encourage the disciples in their faith.
The pastoral theology embedded in episterizo is essential for understanding how the early church grew. Paul and Barnabas's deliberate return visits to Derbe, Lystra, Iconium, and Antioch — explicitly to 'strengthen the souls of the disciples' (Acts 14:22) — reveal that church planting required ongoing pastoral investment, not just initial evangelism. The word implies that young believers need structural support — like a plant staked against the wind. This is the theology behind mentorship, discipleship, and the Pastoral Epistles. The great commission is not merely to make converts but to make disciples, and disciples require strengthening.