Commentaries:
The philosophy of Gnosticism taught that everything physical was evil and that people could attain a higher spiritual understanding through effort. It was the type of philosophy that its adherents thought could be used to enhance or improve anyone's religion. In Paul's letter to the Colossians, we read of this same philosophy having an influence on the church there. It was characterized by strict legalism, a "taste not, touch not" attitude, neglect of the body, worship of angels, and a false humility (Colossians 2:18-23).
Earl L. Henn
Does Paul Condemn Observing God's Holy Days?
Many of the people who had come into the Colossian church had brought their pagan philosophies with them, and they soon began to have an adverse influence on the entire congregation at Colossae. Paul corrects the people in the church who were doing this in Colossians 2:20-23.
Apparently, some of the people had begun thinking that self-imposed asceticism could somehow contribute to their salvation, and had begun turning away from trusting in Christ. They had more faith in their unchristian works. Paul warned them about this in Colossians 2:8: "Beware lest anyone cheat you through philosophy and empty deceit, according to the tradition of men, according to the basic principles of the world, and not according to Christ."
Earl L. Henn
Are the Sabbath and Holy Days Done Away?
The key to grasping this austere regimen lies in the phrase “basic principles of the world” (verse 20; “rudiments” in the KJV). The subject of Paul's teaching does not involve God's laws at all but worldly, pagan teachings that involve asceticism and demon worship. A “rudiment” is a basic, elementary principle or act of worship, and these rudiments are drawn from the world. These ascetic practices have nothing to do with God's true religion. Verse 22 confirms this when Paul writes that these regulations are the decrees and teachings of men, not God.
Paul's counsel on the extreme disciplines of the super-righteous, such as those practiced in the world by ascetics, is that they produce a puffed-up mind—pride, a haughty spirit—rather than humble obedience that truly impresses God, such as that praised so highly in Isaiah 66:1-2:
“Heaven is My throne, and earth is My footstool. Where is the house that you will build Me? And where is the place of my rest? For all those things My hand has made, and all those things exist,” says the Lord. “But on this one will I look; on him who is poor and of a contrite spirit, and who trembles at My word.”
In no way is the apostle teaching that we must not discipline ourselves to live balanced lives within God's laws to avoid sin.
John W. Ritenbaugh
Ecclesiastes and Christian Living (Part Twelve): Paradox, Conclusion
Other Forerunner Commentary entries containing Colossians 2:21:
Genesis 3:1
Galatians 4:9-10
Colossians 1:4
Colossians 2:8
Colossians 2:16-17
Colossians 2:18-23
Colossians 2:20-23