Commentaries:
To paraphrase, Paul is saying, "You had better go back to what you first did, when you first learned the truth. Continue walking in that way, and don't deviate from that path."
John W. Ritenbaugh
The Covenants, Grace, and Law (Part Twenty)
The Colossians were following Christ, but the pressure was on, as Paul had heard from someone else. It may have been Epaphras or Tychicus—or even someone not even mentioned in the book. The word had come to Paul that the Christians in Colosse were undergoing a great deal of pressure, and the pressure was so great that he was afraid they would crack under it—that their faith would give away under the onslaught of the attack. He feared that they would weaken in the faith.
The problem was a deceptive and persuasive philosophy that appeared to have many things in agreement with Christianity. The pressure was not necessarily coming from their pagan neighbors, urging them to stop keeping the Sabbath or the holy days. There may have been some of that happening, but the main problem was a philosophy that had been brought into the church by members from the outside, which they held to be valuable in making Christianity better than what they had received from the evangelists.
John W. Ritenbaugh
The Covenants, Grace, and Law (Part Twenty)