How do we know that believers are complete in Christ?

Paul emphasizes in Colossians 2:10 that 'ye are complete in Him, which is the head of all principality and power.' This completeness signifies that through Christ, believers have full acceptance and are lacking nothing for their salvation. The sufficiency of Christ means that there’s no merit or work required from us; salvation is entirely the work of God through His grace. Therefore, in Christ alone, believers have redemption, righteousness, and all spiritual blessings, and they are fully justified before God.