(This is from a devotion I wrote for Alpha-Omega a few years ago...)
And everyone who has this hope fixed on Him purifies himself, just as He is pure. Everyone who practices sin also practices lawlessness; and sin is lawlessness. You know that He appeared in order to take away sins; and in Him there is no sin. No one who abides in Him sins; no one who sins has seen Him or knows Him. Little children, make sure no one deceives you; the one who practices righteousness is righteous, just as He is righteous; the one who practices sin is of the devil; for the devil has sinned from the beginning The Son of
God appeared for this purpose, to destroy the works of the devil. No one who is born of God practices sin, because His seed abides in him; and he cannot sin, because he is born of God. [1 John 3:3-9 NAS]
This passage speaks about how all of our own efforts to purify ourselves are completely futile. Works-based righteousness will NEVER succeed in making us righteous in God's eyes. Ultimately, our righteousness is only obtained through the work of the Holy Spirit, calling us repentance and belief in Christ alone. Sanctification is God working in us, and us manifesting outwardly that inward working of the Holy Spirit. The legalist would say, "I obtained righteousness myself, and God is happy with what I achieved", when in actuality, the correct attitude of the believer should be one of "God DID IT within me, and I'm forever grateful that he overcame my own sinful, fallen nature in order to do it." One of the things that makes Christianity distinct from all other religions of the world is God's perfect grace, and that our salvation is not based on our own works and perfecting of ourselves, but rather its God who alone perfects us.
I was reading some of Calvin's remarks on the book of I John, and he makes the observation that John "plainly declares that the hearts of the godly are so effectually governed by the Spirit of God, that through an inflexible disposition they follow his guidance" Calvin later continues that "God testifies that he gives a new heart to his children, and promises to do this, that they may walk in his commandments.
We as believers should all take comfort in knowing that God's grace is sufficient in our lives, and that our righteousness is not dependent at all upon us or our works, but instead is solely a gift of God through Christ
Jesus our Lord.