With precisely this aim, to restore in their consciousness the obligation to believe unwaveringly as they first received, St. Paul mentions Epaphras here. He sets forth not Epaphras' personal virtues, but his significance according to the divine economy of salvation on earth. He is my fellow servant, and for you a faithful minister of Christ.
"From him you learned," εμαθετε. He guided you to what you experienced in deed as the grace of God. This would have been enough to keep you faithful to the faith. Yet I add to this that he did not teach you on his own.
The Lord Himself sent me, and I sent him in the name of Christ the Lord. He is a fellow servant, συνδουλος, of Christ with me. We are servants and workers of one Lord. Therefore what he taught you is from the Lord. Do not waver in faith concerning what you received from him.
Blessed Theodoret writes: "The Apostle adorned Epaphras with many praises, calling him beloved, fellow worker, and faithful minister of Christ, so that the Colossians would deem him worthy of greater respect."
Blessed Theophylact explains: "The Apostle called him a beloved fellow servant, showing that he is a man worthy of every confidence. For St. Paul would not have loved him or called him his fellow servant if he had not been a true preacher. He called him a faithful minister of Christ for them, giving them to understand that among them, for their good, he served in works befitting Christ."
That is, he faithfully appropriated to them the divine economy of salvation accomplished by Christ the Lord, as though Christ Himself were accomplishing it. "A minister of Christ for you" also expresses that he is a man of prayer and intercessor for you before Christ.