4 Whoever commits sin also commits lawlessness, and sin is lawlessness. 5 And you know that He was manifested to take away our sins, and in Him there is no sin. 6 Whoever abides in Him does not sin. Whoever sins has neither seen Him nor known Him.
7 Little children, let no one deceive you. He who practices righteousness is righteous, just as He is righteous. 8 He who sins is of the devil, for the devil has sinned from the beginning. For this purpose the Son of God was manifested, that He might destroy the works of the devil. 9 Whoever has been born of God does not sin, for His seed remains in him; and he cannot sin, because he has been born of God.
[The New King James Version (1 Jn 3:4–9). (1982). Thomas Nelson.]
This is a difficult passage to process. If we make sinning or not sinning the measure of who is a Christian, as the passage suggests, we only have a handful of ways to include ourselves in the "Christian" category.
One option is to take the passage at face value and claim that we do not commit any sins. Though this option's fatal flaw is that our own sins and sinfulness is obvious to each one of us, some people do claim they have no sin and prove that they have choosen to deceive themselves (1 Jn 1:8).
Another option is to dig into the passage and try to understand how our sin and sinfulness does not disqualify us from being in the "Christian" category. One way to do that is to differentiate between our sins and sinfulness and those of the lost by saying that lost people practice sin, habitually sin, have a lifestyle of sin, or live in unrepentant sin. Certainly, there is some support for this point of view given the curious translations of the word "ποιέω" ("to do") as "practice". But this point of view yields some untennable positions, like saying that a person who only commits sins occasionally and repents whenever he sins is righteous just as Jesus is righteous (vs 7), or like saying that a person who is born of God can only sin a little because His seed remains in him (vs 9).
The only other option I know of (and the one to which I ascribe) is to understand the passage as contrasting the flesh with the spirit of a person who has been made a new creature through God giving birth to him. The flesh is of the devil, can't cease from sin, and has no righteousness. But the new creation is of God, can't be corrupted by sin, and is righteous just as He is righteous. This is how we differentiate between who we are in Adam and who we are in Christ -- when we see Him in us, see that we are joined to Him, and see that we are one spirit with Him (1 Cor 6:17).