How do we know that salvation is fully achieved through Christ's sacrifice?

When Jesus declared 'It is finished,' He confirmed that all aspects of the redemptive work required for salvation were completed. This means there is nothing we can add to it or need to do ourselves. Ephesians 1:4-5 teaches that believers were chosen in Christ before the foundation of the world, underscoring the divine purpose behind salvation. Our standing before God is based solely on the finished work of Christ, as articulated in 2 Corinthians 5:21, which emphasizes that He became sin for us, so we could be made righteous before God.