For in Christ all the fullness of the Deity lives in bodily form, and you have been given fullness in Christ, who is the head over every power and authority (Col 2:9-10).

Reading the New Testament, we often come across expressions like “in Christ,” “in him,” “in whom,” “by him,” “through him,” etc. Such expressions are especially used exuberantly again and again by Paul in his letters (more than160 times). In the above scripture, Paul first states that “all the fullness of the Deity”—the very essence and qualities of God like his love, holiness, righteousness, might and glory—dwells in Christ who has come in the flesh, and goes on to state that we believers today have come to be filled with the same “fullness” in Christ.

So then, just as you received Christ Jesus as Lord, continue to live in him, rooted and built up in him, strengthened in the faith as you were taught, and overflowing with thankfulness (vv. 6-7).

So, he urges us to live (lit. walk) “in him” having been rooted, and being continually built up “in him.” But what is the meaning of the phrase “in him”? How can we walk in him?

In him you were also circumcised, in the putting off of the sinful nature, not with a circumcision done by the hands of men but with the circumcision done by Christ, having been buried with him in baptism and raised with him through your faith in the power of God, who raised him from the dead (vv. 11-12).

Circumcision was instituted by God as the sign of his covenant (Gen 17): it symbolizes the fact that the one circumcised has entered into the covenant with God and is now bound by the terms of the covenant. However, the circumcision discussed here was “the circumcision done by Christ (lit. the circumcision of Christ)”—his death and resurrection, which our baptism is the symbol of. Baptism was instituted by Jesus under the new covenant as circumcision was under the old covenant: it signifies the spiritual fact that we have been united with Christ in his death and resurrection (cf. Rom 6:3-5). In other words, both the circumcision of Christ and baptism signify the special spiritual status of union that the believers have with Christ. This is the meaning of the phrase “in Christ”: if you are in Christ, you are united with him, and belong to him.

We humans are easily affected by what is around us. What we belong to affects and determines our personality, thoughts and way of life. Thus, what or whom we belong to is very crucial: if you belong to God, you will live and be blessed, but if you belong to Satan, you will suffer and die. Eve chose to have union with Satan by listening to him and accepting his word. Adam followed her by listening to her. By accepting God’s word, you come to be united with God, and by accepting Satan’s word, you come to be united with Satan.

See to it that no one takes you captive through hollow and deceptive philosophy, which depends on human tradition and the basic principles of this world rather than on Christ (v. 8).

Every person has a choice of accepting God’s word or accepting Satan’s word. Jesus, too, was given that choice, and tempted in the same way we are.

The devil said to him, "If you are the Son of God, tell this stone to become bread." Jesus answered, “It is written: ‘Man does not live on bread alone (Luke 4:3-4).’”

Jesus never accepted Satan’s word, but rather, he always had union with the Father by accepting his word. In the same way, all believers should remain united with Christ by having his words remain in them. Know that you are in Christ, and apart from him you can do nothing (John 15:5).