How do we know assurance of salvation in Christ is true?

The assurance of salvation is founded on the belief that Christ's work on the cross is fully sufficient for our redemption. As stated in the sermon, 'It is finished' signifies that nothing can be added to or taken away from His sacrifice. God's promises are fulfilled in Christ, who is our covenant head and surety. Ephesians 2:6 says that believers are 'raised up together, and made to sit together in heavenly places in Christ Jesus,' indicating that believers' salvation is secure in their union with Him. This security is not contingent on our works but on His faithful and complete work.