How do we know that sanctification is by God's grace?

Sanctification is the process by which believers are made holy and set apart by God. In 2 Thessalonians 2:13, we see that God chose believers for salvation through sanctification by the Spirit and belief in the truth. This affirms that sanctification is not a work of human effort but a divine act of grace. The concept of being set apart, as referenced in Jude 1, indicates that God's elect are distinguished by His sovereign choice. This notion is crucial in Reformed theology, emphasizing that our standing before God is due to His initiative rather than any merit of our own. Being sanctified also aligns with the assurance that, through Christ, we are not only forgiven but are also being transformed into His image by the Spirit’s work within us.