When Paul writes that we are complete in Christ he is in the same context warning us about vain deceit and the tradition of men (Col 2:10).
When it comes to salvation Christ has done it all for you. There is nothing else that needs to be added to him.
It is not uncommon for churches to wrongly teach that you need to perform a membership ritual in order to be counted among God’s people. They teach that it is a custom or tradition required by God.
At one time circumcision functioned as the token of entry into God’s people. But Paul says that Christ circumcised you without hands from the body of your sins (Col 2:11).
Likewise people are confused about the need for water baptism in order to be saved.
Yet, Paul makes it clear that our baptism as well as our resurrection is through the faith of the operation of God (Col 2:12). We are baptized into Christ’s death in order to be saved not a pool of water (Rom 6:1-3).
Most common is the teaching that although Christ did so much at the cross we now need to submit to at least a few ordinances of the law in order to prove that we are saved.
Sadly, many are vainly deceived that their church-going, tithing, or good behavior keeps them in the body of Christ.
About this Paul strongly writes that Christ blotted out the ‘handwriting of ordinances that was against us’.
“Let no man therefore judge you in meat, or in drink, or in respect of an holyday, or of the new moon, or of the sabbath days:” (Col 2:16)
It was on the merits of Christ’s shed blood on your behalf that you are saved from God’s wrath. Circumcision, baptism, nor ordinances can add one ounce more to what Christ has already accomplished for you.
What will make you complete and finish the work of salvation is the shed blood of Christ on your behalf. Put your faith in this and nothing else and you will be complete in Christ!
“But to him that worketh not, but believeth on him that justifieth the ungodly, his faith is counted for righteousness” (Romans 4:5)