Paul writes to the church in Colossi, one he has not personally visited and had no hand in founding. He praises the believers for their faith and zeal in Christ, words that form the prelude to an issue that is troubling the church and Paul as well: syncretism, the watering down of the Christian message through the adoption of human philosophic and or scientific principles to explain reality. And so in language that is stirring and emotionally charged, he describes for them the fullness of Christ, that is, He is God, eternally existent. This great God is unique and dwells apart from mankind and yet He lives with His people in the church by His Holy Spirit. And He is truly man as well. He God incarnate who gave His life as an atonement for the sins of man.
This assertion of the divinity of Christ and his reality as a human being are meant to counteract false teachings that take Jesus away from the central part of the faith and put the individual human being there. The Colossians needed to be reminded of the truth because someone was telling them that Jesus was not sovereign God but a lesser deity. Someone is telling them that Jesus did not really come in the flesh, that he only appeared to. Denial of either or both of these principles destroys the whole faith for as Paul points out, they contradict the truth of the atonement. For the death of Christ to be efficacious He had to be both fully God and man. In addition this work of atonement is all of Christ. We add nothing to it by following the Law or by good works.
Today there are many false prophets and teachers who are corrupting the church. They come in the name of Jesus. Many mainstream Protestants and even evangelicals teach a form of universalism. They deny the uniqueness of Christ and His sacrifice in favor of a tolerance for and acceptance of all religions as equally valid. The bigger problem in the evangelical churches is that there is less focus on glorifying God and more on glorifying and exalting the self. Faith is all about exalting Christ and what He has done for us, not what we can do for Him.