Summary: Often we want to make ourselves better but go about it the wrong way. Paul the Apostle gives us tips in how to put off the old nature and put on Christ’s character.
In chapter 2, Paul focused on the error of elevating the mind above the knowledge of God, and focusing on taming the physical body as a way to righteousness. He chastises the use of external rules and regulations, especially those around following certain ritual days and abstaining from certain foods and performing certain rites in order to beat the body and elevate the mind.
He finished that chapter with this admonition:
Colossians 2:23 (quickview)  Such regulations indeed have an appearance of wisdom, with their self-imposed worship, their false humility and their harsh treatment of the body, but they lack any value in restraining sensual indulgence.
See, the argument for legalism and, in this case, a pre-Gnosticism, is that if we don’t tame the body then it, being evil, will be out of control. The problem is that self-imposed rules of behavior don’t really do anything to stop the temptation to sin. If you tell someone that they can no longer eat chocolate, what is the first thing they desire?
The goal of sinless living is good - but the method to get there is wrong. In chapter 3 Paul gives us the proper way to deal with the flesh and mature the mind and spirit - it doesn’t come from secret knowledge that’s basically open to the interpretation of those "in the know" - and it doesn’t involve elevating the mind of man above the mind of God.
In short this chapter consists of the following:
" Lift up your eyes. You’ve been resurrected into a new creature, a citizen of a new country - so put your focus there.
" Put off the old self to death - not by your own efforts but by the cross
" Put on the new self given to you by Jesus - and encourage that new self by taking in of the Lord, giving out in worship, praise, and an outward expression of love in everything you do.
1 Since, then, you have been raised with Christ, set your hearts on things above, where Christ is seated at the right hand of God.
" Where is your heart set? Jesus said "Where your treasure is, there will your heart be also." What do you value? What is treasure to you - money, fame, smarts, power - stuff?
" Galatians 2:20 (quickview)  I have been crucified with Christ and I no longer live, but Christ lives in me . The life I live in the body, I live by faith in the Son of God, who loved me and gave himself for me.
" If you’ve given your life to Jesus Christ then you died on the cross with Him - and that means all that old self died too. You were then resurrected - given a new eternal life not tainted by sin and indestructible.
" It doesn’t mean that you simply don’t know the world around you even exists so you quit your job and lay on the couch all day - it means that what’s important to you are the things that involves your heavenly citizenship - transformation of your self into a new person.
2 Set your minds on things above, not on earthly things. 3 For you died, and your life is now hidden with Christ in God. 4 When Christ, who is your life, appears, then you also will appear with him in glory.