Matthew 24:14

And this gospel of the kingdom shall be preached in all the world - The evidence that this was done is to be chiefly derived from the New Testament, and there it is clear. Thus Paul declares that it was preached to every creature under heaven Colossians 1:6, Colossians 1:23; that the faith of the Romans was spoken of throughout the whole world Romans 1:8; that he preached in Arabia Galatians 1:17, and at Jerusalem, and round about unto Illyricum Romans 15:19. We know also that He traveled through Asia Minor, Greece, and Crete; that he was in Italy, and probably in Spain and Gaul, Romans 15:24. At the same time, the other apostles were not idle; and there is full proof that within thirty years after this prophecy was spoken, churches were established in all these regions.

For a witness unto all nations - This preaching the gospel indiscriminately to “all” the Gentiles shall be a proof to them, or a witness, that the division between the Jews and Gentiles was about to be broken down. Hitherto the blessings of revelation had been confined to the Jews. They were the special people of God. His messages had been sent to them only. When, therefore, God sent the gospel to all other people, it was proof, or “a witness unto them,” that the special Jewish economy was at an end.

Then shall the end come - The end of the Jewish economy; the destruction of the temple and city.