We know we are redeemed through the testimony of Scripture and the inner witness of the Holy Spirit.
The assurance of our redemption comes both from the promises found in Scripture and the internal witness of the Holy Spirit. Romans 8:16 says, 'The Spirit himself bears witness with our spirit that we are children of God.' This relationship assures us that we are indeed redeemed. Furthermore, passages like Ephesians 2 describe how we were once far off but have been brought near by the blood of Christ, confirming our standing as redeemed. Thus, both the objective truth of God's Word and the subjective assurance we receive through the Spirit reinforce our confidence in the truth of our redemption.
Scripture References:
Romans 8:16, Ephesians 2:13, 1 Peter 1:18-19
Commentary