"Let no one keep defrauding you of your prize by delighting in self-abasement and the worship of the angels, taking his stand on visions he has seen, inflated without cause by his fleshly mind." (Colossians 2:18)Paul is not speaking of someone who can actually defraud you of your prize, but he is using what appears to be a sports metaphor. He seems to be referring to an umpire who can declare someone disqualified from the race and, ultimately, from the prize for not competing according to the rules. The English Standard Version of the Bible translates it this way, "Let no one disqualify you." (Colossians 2:18 ESV) and the God's Word Bible translates it as, "Let no one... tell you that you don't deserve a prize." (Colossians 2:18 God's Word)
In life there will never be any shortage of people wanting to judge us and to point out to us that we are doing it wrong, which usually means we are not doing it their way. Some, in their own delusion, may mean well, but their judgment is a snare that can rob us of all that God has for us. God has come to set us free yet, if we submit to such and to their judgment, we will once again find ourselves in bondage. When it comes to things like food, drink, festivals, observances, and the like, we must never allow other to become our judges for only one is our judge, Jesus Christ. Paul says of those who desire to be judges, "Who are you to judge the servant of another? To his own master he stands or falls; and he will stand, for the Lord is able to make him stand." (Romans 14:4) Jesus is our judge, there is no need for another.
As for the rest of the verse, it is unclear to whom Paul is speaking; to the one being defrauded or to the one defrauding. Darby translates this verse as if Paul is speaking to the defrauder, "doing his own will in humility and worship of angels, entering into things which he has not seen." (Colossians 2:18 Darby) while the Message Bible assumes Paul is speaking to the defraudee, "ordering you to bow and scrape, insisting that you join their obsession with angels and that you seek out visions." (Colossians 2:18 The Message) Regardless of which interpretation you choose, the message is the same; there will always be those who choose their own brand of religion and, by it, seek to judge you and compel you to become like them. To them we must not yield lets our religion too become defiled and deluded with mixture.
One of the things Paul specifically warns us about in regard to such men and women who would seek to judge us is a dependence upon self-abasing humility. It seems to me that some religious sects are so dedicated to impressing upon people their lowly and unworthy state that they never allow them to rise above their former selves to experience the newness of life they have in Christ. I have been in churches where, each and every Sunday, the participants are taught to say, "I am not worthy but only say the word and I will be made worthy." Each week they are forced to confess their unworthiness, their disqualifications for the prize, when in reality Christ has already made them worthy! I have also been in some churches where, each week, there is a call for those in attendance to recommit their lives to Jesus or to "get right" with Jesus. Each week they are told they are sinners and that they are not living right and that they need to "come clean" and get right with God. However, Jesus has already cleansed us and bestowed upon us the righteousness of Christ. Such judgement would try to convince us that we are, or have been, disqualified for the prize while the truth is that, we have already been "made... accepted in the Beloved." (Ephesians 1:6 NKJV)
Paul says of true humility that, "you not to think more highly of himself than he ought to think." (Romans 12:3) This also means that we ought not to think more lowly of ourselves then we ought. True humility is knowing who we are, accepting who we are, and living who we are. It's not trying to be someone else or trying to project ourselves as someone else. We will never become that new creation in Christ until we realize that we already are that new creation in Christ. Let us stop listening to those who would tell us that we are unworthy, disqualified, or too damaged to receive this new life in Christ. Instead, let us start living this new life that we have already been given; to be the new men and women we have been recreated in Christ to be. Let our freedom, newness, and abundance be the judge of those who would seek to judge us in return.