In the Bible those who have fallen away in their love and service for Christ are referred to as backsliders—they have slid back somewhat from where they were with the Lord. Many of those who call themselves backsliders may never have been converted at all and are resting on a profession which is now proving to be false. There are those however who are converted; the Holy Ghost lives in them and they know the Lord. Because the seed of the gospel remains in them they feel the backsliding deeply and desire to be free from sin. It is incompatible with what they know they are in Christ.
This response to sin is indeed evidence that we are in Christ and is therefore a great encouragement. The man who walks after the Spirit is a man governed by the indwelling Spirit of Christ. His body is the temple of the Holy Ghost. Christ reigns in him, sin’s reign has been broken, and though he still sins, his sin is a burden to him. He desires to be free of indwelling sin. To walk after the flesh is to be carried along by the dictates of a nature disposed to sin; whereas the Spirit-led man is a man burdened over his sin and who finds freedom from that burden in Christ.