“But now, since you have been set free from sin and have become enslaved to God, you have your fruit, which results in sanctification  — and the outcome is eternal life!” Romans 6:22 CSB https://bible.com/bible/1713/rom.6.22.CSB

In his second letter to the Corinthians, the Apostle challenges the church to test itself to see if it is truly in the faith. In this letter to the Romans, we discover what we are looking for in that test. Christianity is the work of God to save men from the just punishment we deserve and that He must deliver, for He is holy and cannot deny Himself. Yet, not wanting all of us to perish because we are all sin-stained at birth, He rescued us by coming to us as one of us in Jesus the Savior. Living a perfect life, He gave Himself at the cross as the perfect sacrifice to exchange His life for ours. Jesus was punished in the place of all those who bow before Him, confessing their rebellion against God and asking for pardon from His justifiable wrath to come. Having been pardoned, we are now free from the penalty of our sin but not from its presence. The power of sin in our flesh, that which propels us away from God, is being broken by the power of God given to us at our salvation, the Holy Spirit, Who guarantees our safe pass through death and into eternal life with Jesus. The power of God within us, coupled with our choice to surrender our lives to Jesus, denying ourselves, and dying to our rebellious ways, leads to living lives pleasing to God and forms our personal holiness. This holiness is our sanctification, the process of becoming increasingly like Jesus in every way that will reach its grand conclusion when we see Him and He fits us with a new body free from the presence of sin. So if we are God’s servants as Jesus was, living more and more like Jesus did, serving God by doing His will on earth as it is in heaven, we are passing the test and know with certainty we are children of God, even feeling the Holy Spirit’s delight in us affirming our love for God.