Already preached to all creatures?

It is well known from the Scripture that the gospel must first reach all nations before the end comes. The great commission of Jesus Christ to his disciples is to preach the gospel to all nations. And we are still working on that commission today. But, in Colossians 1:23, we saw something interesting, which seems to indicate that the task was already accomplished even in the time of Apostle Paul:

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; Colossians 1:23, KJV

This of course is very puzzling at the first glance, but the key seems to be in the prophesy of Zechariah the father of John the Baptist, when he was filled with the Holy Ghost:

Blessed be the Lord God of Israel; for he hath visited and redeemed his people, and hath raised up a horn of salvation for us in the house of his servant David; as he spake by the mouth of his holy prophets, which have been since the world began: Luke 1:68-70, KJV.

Paul also wrote in the book of Hebrews, testifying that those of the old times had the same gospel as we have now:

For unto us was the gospel preached, as well as unto them: but the word preached did not profit them, not being mixed with faith in them that heard it. Hebrews 4:2, KJV

And indeed, the gospel was pronounced even when Adam and Eve fell, because the Lamb of God was slain at the foundation of the world (ref: Revelation and Ephesians). Now in the end times, this mystery is fully manifested to us, and this gospel of salvation should be preached among all nations, to have them know the fulfillment of the word of God, to have hope of eternal life, till the end comes:

whereof I am made a minister, according to the dispensation of God which is given to me for you, to fulfil the word of God; even the mystery which hath been hid from ages and from generations, but now is made manifest to his saints: to whom God would make known what is the riches of the glory of this mystery among the Gentiles; which is Christ in you, the hope of glory. Colossians 1:25-27, KJV.

It is only that the gospel is now fully manifested, but the same gospel was preached from the very beginning to all men, only that most of them hardened their hearts and rejected it quickly, and followed their own ways of this world. Hey, but now it is high time to tell everybody what our Lord Jesus said on the cross: it is finished!