How do we know that the church's sanctification is true?

Scripture provides assurance of the church's sanctification, particularly in passages like Ephesians 1:4-5, where it states that believers were chosen in Christ before the foundation of the world to be holy and blameless. This divine act indicates God's eternal purpose for the church. Additionally, when the gospel is preached, the Holy Spirit works in believers' hearts to confirm this sanctification, leading them to recognize their need for Christ and to trust in His righteousness, validating their holy calling as members of the church.