Each part of the body of Christ has an important role and helps other parts grow. Christ, the head of the body, works through each part. He makes them fit together. He is the ultimate source of growth (see Colossians 2:19).
When all believers serve effectively, the whole body will be healthy, growing, and full of love (compare 1 Corinthians 8:1). Love is the most important factor in Christian growth (1 Corinthians 13:1–13).