Question: In view of Romans:1:8; Colossians:1:6,23, and Acts:17:6, it would appear that all the world has already heard the gospel and heard it within the first 50 or so years after our Lord returned to heaven. The world's inhabitants continue to increase in number, so this would seem to be an unattainable task. What am I missing?
Response: The verse reads, "First, I thank my God through Jesus Christ for you all, that your faith is spoken of throughout the whole world." It is the disciples' "faith" that is spoken of. That is, in general terms, their faith is known and commented upon. It is clear from the context that "world" as used in Romans:1:8 (for example) doesn't mean the entire earth but is limited to the "world" of the Roman Empire. Much the same could be said of Acts:17:6, when the Thessalonians spoke of the disciples as having "turned the world upside down." They were simply saying that wherever the disciples had gone, the "world" system was impacted, as in Ephesus (Acts 19) where the idol makers' craft was "in danger" because of the preaching of the gospel (Acts:19:27).
The gospel is not convenient to the world system and cannot coexist with it. In Colossians:1:6,23, Paul is again speaking of the known world (i.e., the Roman Empire) into which the gospel has gone. In verse 6, Paul writes that the gospel "bringeth forth fruit" wherever it has been preached. Colossians:1:23 reads, "...if ye continue in the faith grounded and settled, and be not moved away from the hope of the gospel, which ye have heard, and which was preached to every creature which is under heaven; whereof I Paul am made a minister."
It is the "hope of the gospel" that has been "preached" to every creature under heaven. God has certainly left a general witness of Himself for every individual in the world.
Titus:2:11-12 tells us, "For the grace of God that bringeth salvation hath appeared to all men, teaching us that, denying ungodliness and worldly lusts, we should live soberly, righteously, and godly, in this present world."
In Psalm 19 we learn, "The heavens declare the glory of God; and the firmament sheweth his handiwork. Day unto day uttereth speech, and night unto night sheweth knowledge. There is no speech nor language, where their voice is not heard. Their line is gone out through all the earth, and their words to the end of the world. In them hath he set a tabernacle for the sun" (vv. 1-4).
Paul writes in Romans, "For the invisible things of him from the creation of the world are clearly seen, being understood by the things that are made, even his eternal power and Godhead; so that they are without excuse" (1:20).
Although it can be reliably stated that the gospel during the lives of the first apostles was taken as far as India and China, nevertheless, Paul still knew that there were "regions beyond" (2 Cor:10:16) where the gospel had not yet gone.
Regarding the attainability of the Great Commission, we have nothing less than the promise of the Lord Jesus Christ, who prophesied, "This gospel of the kingdom shall be preached in all the world for a witness unto all nations; and then shall the end come" (Mt 24:14).