"Cheat you" - the margin gives a better rendering of the original word, "plunder you", or "take you captive" (compare NIV). They were in danger of being taken prisoner and being carried away into exile from the truth.
What is clear and definite in New Testament teaching is that no system devised or conceived by man can be in harmony with God's salvation planned and perfected in Christ (Jude 3 ). That would be the means of Satan as a thief and destroyer (John 10:10
), of distorting and blinding from the truth so that he could carry the deceived into the slavery and damnation of error. Therefore be on guard against hollow and deceptive philosophy that depends on human tradition and the basic principles of this world.
"The fulness" (See comment on Colossians 1:9 ). In Christ there dwells all the fullness of the Godhead.
"Bodily" points us to the stupendous fact that He is the eternal "word;" became incarnate and tabernacled among us (John 1:14 ); died for us, rose again, and in that same body ascended (Hebrews 9:24 ). The fullness of the Godhead forever in Him bodily,
so that He who is ever God will not cease to be man, whom one day we will see (Acts 1:11; Romans 9:5; Philippians 3:20 ).
Christ Himself is the fountain head of all we need. All other manmade cisterns are broken, useless, and mere pretensions. "In Him" - to be outside is to be without. But we receive His fullness because we are in Him. Completeness is enjoyed living in the fountain. As
"head of all" Christ Jesus cannot be rivalled or replaced. He is supreme Lord and in Him we have all sufficiency. (Colossians 1:16 ).
Whereas physical circumcision was partial and a sign - spiritual circumcision, made without hands, describes the fullness given in Christ. In Christ,
Our fullness of salvation is witnessed to in baptism by immersion, which demonstrates our identification with Him. (Galatians 2:20 ). We were buried with Him, so have ended our old life of sin, and are shut off from the kingdom of Satan, by participation in His
death. As partakers of His resurrection power, victory in living is attained by His life in us. Our union with Christ brings life victorious and abundant. So complete are we in Him that no other revelation is necessary or possible. Christ is our life - it is impossible to live
without Him.
Vital life in Christ is not to be substituted for ritual abstinence in food and drink (Colossians 2:16 ). In Christ we are freed from this yoke of bondage (Acts 15:10 ). We should enjoy our liberty with thanksgiving.
Substance that is of Christ must not be substituted for the shadow of ritualistic days (Colossians 2:16 ). The holy days of Mosaic ritual are superseded by the reality we have in Christ. "But the substance is of Christ" (Colossians 2:17 NKJV). Note that
substance 'soma' literally is body. The reality we have is relationship with Christ as His body - members in particular of His body the Church. No ritualistic days or ceremonies are to substitute for the spiritual living communion with the Lord.
Do not allow yourself to be robbed of directly relating to Christ. You need no ritualistic humility nor angelic mediators (Colossians 2:18 ). Do not be deceived by self-deceived men who build their teaching on fantasy, not fact.
Do not allow proud, fleshly men to bring you into the folly of heresies, and forbidding the worship of the Creator (Colossians 2:18 ). Such do not receive grace and are resisted by God (James 4:6 ).
Do not, like these false teachers, pretend attachment to Christ. Your vital union to the Head must be real. (Colossians 2:19 ). Those who do not hold fast the Head are cut off from the true source of spiritual life and sustenance, unity and growth.
7. A FORTHRIGHT CHRIST CENTRED DECLARATION
(COLOSSIANS 2:8-23)
7.1. WARNING TO BE ON GUARD (Colossians 2:8)
Colossians 2:8 "Beware lest anyone cheat you ..."
Colossians 2:8 "... through philosophy and empty deceit, according to the tradition of men, ..."
"This term (which occurs also in Colossians 2:20 and Galatians 4:3,9) means false, worldly, religious elementary teaching. Paul was counteracting the Colossian heresy, which, in part, taught that for salvation
one needed to combine faith in Christ with secret knowledge and with manmade regulations concerning such physical and external practices as circumcision, eating and drinking, and observance of religious festivals." NIV
Study Notes
7.2. DECLARATION OF ABSOLUTE DEITY (Colossians 2:9)
Colossians 2:9 "For in him dwelleth all the fulness of the Godhead bodily."
"not merely the divine attributes, but the divine nature itself". J.A. Bengel - New Testament Word Studies -
Kegel
"The declaration that the very essence of deity was present in totality in Jesus' human body was a direct refutation of gnostic teaching." NIV Study Notes
7.3. OUR FULLNESS IS IN CHRIST ALONE (Colossians 2:10)
Colossians 2:10 "And ye are complete in him, which is the head of all principality and power:"
7.4. DESCRIPTION OF FULLNESS IN CHRIST (Colossians
2:11-15)
Colossians 2:11 "In Him you were also circumcised with the circumcision made without hands, by putting off the body of the sins of the flesh, by
the circumcision of Christ,"
"the whole corrupt, carnal nature is put away like a garment which is taken off and laid aside". Mavin R. Vincent - Word Studies in the N.T.
Macdonald N.D
Colossians 2:12 "Buried with him in baptism, wherein also ye are risen with him through the faith of the operation of God, ..."

In Him alone is life "alive together" (Colossians 2:13 ). 
In Him alone is forgiveness (Colossians 2:13 ). 
In Him alone condemnation is removed (Colossians 2:14 ) (by the blood of His cross). 
In Him alone is triumph over Satan, principalities and powers (Colossians 2:15 ). "Christ crucified and risen is Lord of all; all the forces of the universe are subject to Him, not only the benign ones but the hostile ones as well. They are all subject to Him as their Creator, the latter are subject to
Him also as their conqueror. And therefore to be united to Him is to be liberated from their thralldom, to enjoy perfect freedom, to overcome all the power of evil because Christ's victory is ours". F.F. Bruce -
Romans - Tyndale, 1963
7.5. FREEDOM FROM ALL SUBSTITUTES (Colossians 2:16-
17)
7.5.1. THAT OF RITUALISTIC EATING
1 Timothy 4:4 "For every creature of God is good, and nothing to be refused, if it be received with thanksgiving:"
Romans 14:17 "for the kingdom of God is not eating and drinking, but righteousness and peace and joy in the Holy Spirit."
7.5.2. THAT OF RITUALISTIC DAYS
7.6. ATTACHMENT TO CHRIST THE HEAD MUST BE ACTUAL
(Colossians 2:18-19)
Colossians 2:18 "... intruding into those things which he hath not seen, ..."
"In the Colossian letter the vital connection with the head is the main theme; in Ephesians, the unity in diversity among the members". Lightfoot