When one reads the Epistle of First John in the English translation (KJV), the reader may draw the conclusion that John not only contradicts himself but that he establishes an impossible test in determining the genuineness of one’s Christian profession, that being “Christian perfection.” It appears the aged Apostle contradicts himself when one reads what he states in 2:1 compared with 3:9. Is this the case or is there a satisfactory explanation as to what John meant?
In I John 1:8 he makes it clear that all men are sinners and only the provision of Jesus is able to forgive our sins. John writes in 1:8, “If we say that we have no sin, we deceive ourselves and the truth is not in us.” This could be called John’s equivalent to what Paul stated in Romans 3:23, “All have sinned and come short of the glory of God.” All men are sinners and need a Savior. And for one who recognize their sinfulness John writes, “If we confess our sins, he (Father/Jesus) is faithful and just to forgive us our sins, and to cleanse us from all unrighteousness.” (1:9).
Now once one is a Christian John expresses his desire, “My little children, these things write I unto you that ye sin not” (2:1a). That is the goal, the desire, to sin not. But what if as Christians we do sin? John gives us good news, “And if any man sin, we have an advocate with the Father, Jesus Christ the righteous (2:1b). When a Christian does sin we have a lawyer, a go-between, an intercessor, and one who pleads our case before the Father who secures our forgiveness, Jesus Christ the righteous. While the goal, desire and ideal is not to sin, John realizes that as finite creatures the reality is that at times we will sin, but Christ has made provision by His Advocacy to secure our forgiveness and restore our broken fellowship with the Father.
Now when we come to I John 3:9, the Apostle makes a startling statement which appears to contradict what he stated in I John 2:1. In the KJV 3:9 reads, “Whosoever is born of God doth not commit sin; for his seed remaineth in him: and he cannot sin, because he is born of God.”
In 2:1 John recognizes that no Christian measures up to the ideal of not sinning; therefore, the need for an Advocate. However, as 3:9 is translated in the KJV it appears John is saying the proof we are genuine Christians is that we don’t sin anymore! Is John advocating Christian perfectionism as to whether we are saved or not? To gain a proper understanding of the verse let us look at in its context by examining I John 3:4-9, which reads, “4 Whosoever committeth sin transgresseth also the law: for sin is the transgression of the law. 5 And ye know that he was manifested to take away our sins; and in him is no sin. 6 Whosoever abideth in him sinneth not: whosoever sinneth hath not seen him, neither known him. 7 Little children, let no man deceive you: he that doeth righteousness is righteous, even as he is righteous. 8 He that committeth sin is of the devil; for the devil sinneth from the beginning. For this purpose the Son of God was manifested, that he might destroy the works of the devil. 9 Whosoever is born of God doth not commit sin; for his seed remaineth in him: and he cannot sin, because he is born of God.” (KJV)
In 3:4 John says sin manifests itself in lawless rebellion and willful defiance of God, His character being expressed in the Law. In 3:5 John proclaims that Christ, who had no sin, came to earth for the purpose of taking away our sins. In 3:6 John informs us as Christians we need to abide in Him so we will not keep on doing sin. Let it be pointed out the Greek word translated “abide” is a present active participle, meaning to continually remain or abide in Him. The word translated “sin” in the Greek is present indicative active, indicating continual action. In other words, John says in 3:6 if you are not continually abiding in Christ but instead are living in continual sin, you don’t know Him! In 3:7 John says those that continually “doeth” righteousness (“do” Gk poieō) – present active participle, indicating habitual action) prove they are righteous. In 3:8 he writes that those who continually commit sin are of the devil. Again, the Greek word translated “committeth” is a present active participle, indicating habitual action. Then in 3:9 John writes that whosoever is born of God does not continually commit sin, doesn’t live a habitual lifestyle of sin. Once again, the word translated “commit” is a present active participle, meaning one born again doesn’t live a lifestyle of sin. The reason the Christian doesn’t live a lifestyle of sin, is God’s seed, His divine life, remains in the believer (3:9). The life principle of Christ indwells the believer who instills within the Christian the desire to flee from sin and enables the Christian to live a victorious life whereby sin is not the habit or way of one’s life.
Now we come to the translation that appears contradictory and has created controversy. John adds in 3:9 that because the “seed” of God abides in the believer, “he cannot sin, because he is born of God.” The Greek phrase is οὐ δύναται ἁμαρτάνειν (ou dunatai hamartanein).While “he cannot sin” or “not able to sin” is a strict translation it fails to bring out the true thought that is consistent in 3:4-9 and is revealed in the Greek tense of hamartanein. As has been pointed out, the word translated “commit” in verse 9 is a present active participle, denoting action that is habitual. Gleason Archer insightfully comments, “In one respect this otherwise adequate translation fails to bring out one very important feature of the hamartanein (to sin) after ou dynatai (not able), a present infinitive in Greek implies continual or repeated action.”  In other words, no one who is born of God engages in a lifestyle sin. To do so is proof one hasn’t been born of God.
S.M. Baugh also points out that the phrase ou dunatai hamartanein, translated “cannot sin,” is a present infinitive. Baugh writes, “The fact that John chose to use the present infinitive…shows he was thinking about ‘sinning’ in v. 9 as a characteristic action. Hence, John does not teach ‘perfectionism’ that Christians can experience sinlessness in this life. Rather, when he says ou dunatai hamartanein he teaches that the genuine Christian cannot be characterized by a life of unrepentant sin.” 
Kenneth Wuest succinctly writes that “cannot sin” in verse 9 is “the present infinitive, [which] in Greek speaks of continuous, habitual action, never the mere fact of the action…The translation therefore is, ‘He is not able to habitually sin.’ The Greek text here holds no warrant for the erroneous teaching of sinless perfection.” 
While there are other explanations which seek to explain 3:9, the above explanation as to what is meant by the translation “cannot sin” is both consistent with the thought of John of in 3:4-9 and doesn’t contradict 2:1. While for this writer the KJV is the preferred translation for reading and studying, I John 3:4-9 in the ESV gives a good sense of what John is seeking to convey: “4 Everyone who makes a practice of sinning also practices lawlessness; sin is lawlessness. 5 You know that he appeared in order to take away sins, and in him there is no sin. 6 No one who abides in him keeps on sinning; no one who keeps on sinning has either seen him or known him. 7 Little children, let no one deceive you. Whoever practices righteousness is righteous, as he is righteous. 8 Whoever makes a practice of sinning is of the devil, for the devil has been sinning from the beginning. The reason the Son of God appeared was to destroy the works of the devil. 9 No one born of God makes a practice of sinning, for God’s seed abides in him; and he cannot keep on sinning, because he has been born of God.” (ESV)
John is clear that those who live a lifestyle of sin, who habitually practice sin, are not saved and are not genuine followers of Christ. It might be added, in order the Christian not find a loophole to sin C.H. Dodd has astutely suggested, “The apparent contradiction is probably not to be eliminated, though it may be qualified, by grammatical [astuteness].”  The Christian’s life should be markedly different from an unbeliever. For one to say they are a Christian and live in habitual sin, John doesn’t mince words, “You are a liar and the truth is not in you” (1:8-10). The teaching of John through his epistle refutes those who contend that because of grace one can live a life of habitual sin. Let it not be so in our lives, but instead heed the words of John, “And now, little children, abide in him; that, when [Christ] shall appear, we may have confidence, and not be ashamed before Him at His coming” (I John 2:28).
 Gleason Archer, Encyclopedia of Bible Difficulties (Grand Rapids, MI: Zondervan, 1982), 428-429
 S.M. Baugh, A First John Reader, (P&R Publishing, 1999), 50-51.
 Kenneth Wuest, “I John,” In These Last Days (Grand Rapids, MI: Eerdmans Publishing, 1957), 150.
 C. H. Dodd, “The Johannine Epistles,” The Moffatt New Testament Commentary (London, 1946), 80.