The greatest secret in the universe has been revealed to humanity: Jesus himself (Col 2.2-3). This is perhaps a hint that the groups harassing the believers at Colossae were Gnostic as well as Jewish. Gnostics were all about secret knowledge and asceticism (at least in this group, cf. 2.18). Paul addressed the Jewish elements in this section too. I’m certainly not dogmatic about this, but it does seem possible that at least elements of Gnostic thought were influencing Colossae, on top of the pervasive traditionalism of the Jewish Christians.
Either way we should pay attention to an important point — all of humanity from the dawn of civilization has been trying to figure out what a specific something is. We’ve always been impressed with a sense that something bigger than us is out there. Since we’ve recently been able to take a crude glimpse into the cosmos itself, we’ve only been more impressed with how powerless we are on this little blue marble. Cosmic scales are something we can’t even wrap our minds around. There’s so much raw power that can only be viewed from distances so vast that we could never hope to travel them physically (eg. supernovas). But a simple cometary fragment could wipe out our little rock, if God willed it!
Most early civilizations deified some element or other natural force on this planet, or they deified what they could observe with the naked eye in the heavens. Many ancient cultures worshipped powerful or beautiful animals, stars, or even political/military celebrities (sometimes all of the above). They were searching everywhere, desperate to find the source of infinite cosmic power, wisdom, and guidance that they instinctively knew existed, but could not identify. Since God is invisible (cf. 1.15), he had to be revealed to us. This great mystery was solved once and for all with the arrival of Jesus on the planet he created (2.16-17). He is that power, and he cares about us! That means he wants to take us with him when this earth is destroyed (2.18-20). The mystery is far more profound (and practical and humbling) than we thought. What is that thing every ancient culture has tried to identify and worship? The Great Mystery of the Eons — Jesus: Creator, Teacher, Civilizer, Rescuer, God.
This message is the secret truth that was hidden since the beginning of time. It was hidden from everyone for ages, but now it has been made known to God’s holy people. God decided to let his people know just how rich and glorious that truth is. That secret truth — which is for all people — is that Christ lives in you, his people. He is our hope for glory (2.27).