The word means, “The state of no deficiency!” Paul counters the errors the believers were facing: Humanism, Legalism, Mysticism, and Asceticism which the believers were told needed to be “added” to Christ if they were to experience “full salvation.” The believers were told their salvation was deficient. Paul counteracts these lies, “works based salvation” with the unchanging truth concerning the believers position In Christ!
There is no deficiency in Jesus Christ the Person, His work, and salvation… therefore there is no deficiency in the salvation He imparts! They are “COMPLETE!” Consider your position that In Christ you have Complete Salvation, Complete Forgiveness, Complete Freedom as a result of your position, “In Christ.” – Colossians 2:8-23