What the Bible says about False Doctrinal Changes
(From Forerunner Commentary)
The key here is "which you heard before." Before what? Before this philosophy (Colossians 2:8) became a problem, or perhaps before their conversion—since hearing the gospel led to their conversion. Paul is taking them all the way back to the beginning because he wants to remind them of what they had faith in then.
The same principle is at work in our lives now. Those who have been devastated through false doctrinal changes have to be taken back to the faith once delivered (Jude 3) to begin rebuilding their faith or they will never recover. Paul was faced with a somewhat similar situation. So He writes, "Brethren, let us go back all the way to the beginning and remember what we heard in the gospel." In this case, apparently, it was preached by Epaphras.
John W. Ritenbaugh
The Covenants, Grace, and Law (Part Twenty-One)