Whoever abides in Him does not sin. Whoever sins has neither seen Him nor known Him. 1 John 3:6
The Bible makes two things clear about sin. First, living a lifestyle of sin indicates that you are not walking in the power of the Holy Spirit, regardless of what you say about your spiritual condition. You cannot regularly spend time studying and meditating on God’s word, praying and walking in fellowship with the Holy Spirit, and persist in sin.
Second, if you do not hate sin the way God does, then you do not truly know Him. There are those who continue in their sin yet insist that they love God and belong to Him. John makes it clear: If you have a lifestyle of sin, you have not seen Him and do not know Him. You may have prayed a “sinner’s prayer,” or made a commitment in your church, or been baptized, but the evidence of the Holy Spirit’s presence in your life is that you are defeating sin. This does not mean that you will never sin, but it does mean that you refuse to make sin a lifestyle and you immediately seek forgiveness when you sin (1 John 1:10). It means that you are opposed to sin, as God is, and you allow the Holy Spirit to eradicate every trace of sin in your life. It means that when you sin, you immediately confess it and repent of it and do whatever is necessary to avoid repeating your sin.
If you find yourself falling into sinful habits or not grieving over your sin as you once did, this indicates that you are not abiding in Christ. Return to Him in repentance; restore your fellowship with Him, and you will once again experience victory over your sin.