From pros (to, toward) + tithēmi (to put, place). Prostithēmi means to add to, place in addition, increase, to do again, to give more. Used for numerical increase of the church, adding to teaching, and the gracious 'adding' of God's kingdom gifts.
The word prostithēmi appears in Acts as the signature term for church growth: 'The Lord added (prosetithei) to their number daily those who were being saved' (Acts 2:47). The passive voice is theologically significant — it is God who does the adding. The church grows not by human strategy alone but by divine initiative. Acts 5:14: 'more and more men and women believed... and were added to their number.' This divine-passive growth language shapes the NT understanding of mission: the church scatters seed (Mt. 13), plants and waters (1 Cor. 3:6), but God gives the auxanō (increase) and does the prostithēmi (adding). Matthew 6:33 uses the same verb: 'Seek first his kingdom and his righteousness, and all these things will be added (prostethēsetai) to you.' The kingdom-first life is the life of divine addition — God keeping the accounting of what we need.