If we as Christians organized ourselves with the purpose of reaching the world for Christ, it would not be long before the entire world would come to know Jesus Christ as their personal Savior.
If one person reaches one for Christ, then there are two. If each one reaches one, then there are four. If this trend continues daily, then by day 33, 8.5 billion people will have heard the Gospel and been won to Christ.
This is the population of the world.