Understanding the Message of Christ is essential to fulfilling his mission. Our duty is to "proclaim Christ" (Colossians 1:27-28). Only the message of Christ is "the word of truth" and "the faith" (Colossians 1:5-6, 23).
Paul is worried that the Colossians will turn aside from this teaching and become captives of false doctrines and commandments. How important it is, therefore, that we understand the message of Christ and are able to distinguish it from the many false messages in the world.
What is the Message of Christ? We answer this question broadly in the three points below. However a simple answer to this question is that the message of Christ is what he said about himself and what he commands us to do, both to become "holy and blameless before him", and to "continue in the faith firmly established" (Colossians 1:12-23).
Colossians 1:5-6,12,23
The hope of eternal life in heavenly glory depends upon the message of the gospel. Paul writes about "The hope laid up for you in heaven, which you heard before in the word of the truth of the gospel" (Colossians 1:5-6). He shortens this, when he mentions it again later, to simply "the hope of the gospel" (Colossians 1:23).
The hope of Heaven is not like the hope of winning a lottery. It is not chancy. It is more like the hope of an inheritance. It is yours already and you simply wait patiently for it to come and do the right thing in the meantime. You can trust it, plan on it, and work toward it with certainty and expectation.
So Paul speaks of this hope as "the inheritance of the saints in light" and says that the Father has qualified Christians to share in this inheritance and they should already be thanking him for this glorious hope and expectation (Colossians 1:11-12).
Colossians 1:25-27
Paul preached the revelation of the mystery which was "hidden for ages and generations but now has been revealed". (Colossians 1:26). Of course God's purpose, the promise that Messiah would come, and the hope of eternal life have always been known.
This hope was "hidden" in the sense that it was mysterious and obscured, a bit like looking up from the bottom of a hill at a garden with a picket fence. You can see the garden is there, but there's a lot of fence in the way of your vision. Peter explains this "mystery" concept very well (1Peter 1:10-12).
Paul uses the analogy of "shadows" versus "the substance" as another way of expressing the former mystery compared to the present clear revelation (Colossians 2:16-17). The Old Testament religion and prophecy showed the shadow of Christ. The gospel reveals Christ himself.
On one of my favourite walks, the path passes beneath some great oaks. On a clear winter's night the moon casts shadows of the leafless branches, making a beautiful, mysterious, and entrancing pattern on the ground. When this is at its best, I have to stop walking and be still for a few moments, taking in all the magic of this dark tracery.
When I look up to the source of this mystery, I see the real oaks only dimly against the moonsky. I can walk the same path in Spring in full sunshine, and what a different sight then! The grand old oaks themselves are seen in all their glory, their spreading branches clothed in verdant new leaf, and full of songbirds rejoicing. This is like the shadows that the people of past ages and generations saw, and the clear revelation that the gospel provides.
In Colossians Paul speaks of two revelations...
The second revelation is possible only through the first. No other message will result in glory at the second coming of Christ.
Colossians 2:6-8
There is human philosophy, and there is the gospel. The former doesn't get you to heaven. The latter does. Paul goes on to warn, "Let no one judge you... Let no one defraud you..." by man-made commandments and doctrines (Colossians 2:16-23). In Paul's time, false religion came from two main sources:
Today these influences, along with philosophies such as evolutionism and humanism, still attempt to change the gospel of Christ, sometimes subtly, sometimes radically, but always making it into a new and different message (and therefore "of no value") rather than the true and original message of the Messiah.