People who follow Jesus Christ are different (2 Corinthians 5:17).  They have chosen to be as unresponsive as Jesus Christ to the way of living that is based on satisfying sensual feelings (Romans 6:6).     It is sometimes a tough call to obey Jesus rather than please ourselves, but even Christ did not please Himself (Romans 15:3).  Some took this to mean that ‘spirituality’ is achieved by religiously following rules of self-denial, punishing their bodies for the good of their souls.  Such practices were part of pagan worship and appealed to people who wanted to feel better about themselves.  But why did some Christians think it was good to behave like those whose hope is in themselves (and people who can help them), whose motivation is self-gain, and whose reason for living is ‘becoming somebody’, gathering attention and praise from others?  They had lost connection with Jesus (Colossians 2:19).
 
Everybody’s lifestyle is based upon what they believe.  We all initially believe what we are taught by our parents, teachers, and mentors.  In this way, family and cultural traditions, and professional and business practices are passed to the next generation.  But when it comes to what pleases God, if the teaching is not true to God's Word, the lifestyle will be ungodly even if it appears 'spiritual'.  If our hearts do not desire God’s will, as revealed in the Bible, our bodies will not be able to hold back from satisfying themselves and displeasing the Lord (James 1:14-15).

The Apostle Paul's plea to the Colossian church is that they should reject ‘spiritual’ instruction that is based on human wisdom, and not on Christ.  Although such teachers will appear to be holy, even to the point of harshly treating themselves, their humility and worship is false because they are exalting their own ideas and not the Lord.  Their teaching can never produce Christ-like living because it rejects the supreme authority of the suffering Saviour.  
 
There is no good prize for being naïve.  As individuals and churches, we are responsible to follow Christ alone.  Self-imposed suffering to 'purify the body and soul' is not the gospel of Christ.  If suffering does come our way, He will give us strength; if we face opposition, He will give us grace (2 Corinthians 12:9).  But in everything, the true believer desires the glory to go to Christ - because He alone is the source of our strength, the companion on our journey and the One who will return for us one day.  True believers will reject any teaching which promises glory today through human effort.  As Jesus said, "Be careful not to practice your righteousness in front of others to be seen by them. If you do, you will have no reward from your Father in heaven." (Matthew 6:1).