1 John 3:9 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.
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Cannot sin. Or, “is not able to go on sinning,” or “is not able to go on habitually sinning.” This does not mean that the Christian is incapable of committing a wrong act. If he were unable to sin, there would be no virtue in his being without sin, and there would be no true development of character. John has already implied that he will make occasional mistakes (see on ch. 2:1). The passage means that, having been born of God, and having God’s life-giving power dwelling in him, he cannot continue his old pattern of habitual sin. He now follows the sinless ideals that have been implanted in his soul by the new birth.
SDA bible commentary
You quoted 1 John 3:9,
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.
A true believer has been transformed so that they cannot live in a pattern of continual sin. This doesn't mean that Christians are ever completely free from sin in this life. (Read and understand Romans 7, and 8)
1 John 1:8–10
If we say that we have no sin, we deceive ourselves, and the truth is not in us. If we confess our sins, he is faithful and just to forgive us our sins, and to cleanse us from all unrighteousness. If we say that we have not sinned, we make him a liar, and his word is not in us.
(emphasis added)
You must always consider CONTEXT when studying Scripture. Otherwise, you can easily fall into error (in this case, "Perfectionism"). (2 Tim 2:15) Here is the whole passage you quoted:
Whosoever committeth sin transgresseth also the law: for sin is the transgression of the law. And ye know that he was manifested to take away our sins; and in him is no sin. Whosoever abideth in him sinneth not: whosoever sinneth hath not seen him, neither known him.
Little children, let no man deceive you: he that doeth righteousness is righteous, even as he is righteous. 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. 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 this the children of God are manifest, and the children of the devil: whosoever doeth not righteousness is not of God, neither he that loveth not his brother.
1 John 3:4-10
Here is 1 Jn 2:1
My little children, these things write I unto you, that ye sin not. And if any man sin, we have an advocate with the Father, Jesus Christ the righteous: And he is the propitiation for our sins: and not for ours only, but also for the sins of the whole world.
1 John 2:1-2
What follows was lifted from one commentary:
In these verses John sets forth, for the third time, the “moral” test of genuine gospel-belief. John speaks of true believers as “practicing righteousness” (v. 7) as opposed to “practicing sin” (vv. 4, 8). While we still sin as believers (cf. 1:8–2:1), a genuine believer does not “practice sinning” (i.e., have a life pattern of sinful pursuits without correction or remorse) because he has been “born of God” and therefore has a completely new identity (3:9; cf. Gal. 3:26; 2 Cor. 5:17). Anyone who does “practice sinning” not only has no grounds for assurance of being in a right relationship with God (1 John 3:10) but also is shown to be still in darkness and at enmity with God, being “of the devil” (v. 8). 1 John 3:1
(Source: Gospel Transformation Study Bible)
In addition,
tn The problem of the present tense of ποιεῖ (poiei) here is exactly that of the present tense of ἁμαρτάνει (Jamartanei) in 3:6. Here in 3:9 the distinction is sharply drawn between “the one who practices sin” in 3:8, who is of the devil, and “the one who is fathered by God” in 3:9, who “does not practice sin.” See S. Kubo (“I John 3:9: Absolute or Habitual?” AUSS 7 [1969]: 47-56) for a fuller discussion of the author’s argument as based on a sharp antithesis between the recipients (true Christians) and the opponents (heretics).
sn Does not practice sin. Again, as in 3:6, the author is making a clear distinction between the opponents, who as moral indifferentists downplay the significance of sin in the life of the Christian, and the recipients, who as true Christians recognize the significance of sin because Jesus came to take it away (3:5) and to destroy it as a work of the devil (3:8). This explanation still has to deal with the apparent contradiction between the author’s statements in 2:1-2 and those here in 3:9, but this is best explained in terms of the author’s tendency to present issues in “either/or” terms to bring out the drastic contrast between his readers, whom he regards as true believers, and the opponents, whom he regards as false. In 2:1-2 the author can acknowledge the possibility that a true Christian might on occasion sin, because in this context he wishes to reassure his readers that the statements he has made about the opponents in the preceding context do not apply to them. But in 3:4-10, his concern is to bring out the absolute difference between the opponents and his readers, so he speaks in theoretical terms which do not discuss the possible occasional exception, because to do so would weaken his argument.
tn Both the first and second ὅτι (Joti) in 3:9 are causal. The first gives the reason why the person who is begotten by God does not practice sin (“because his seed resides in him).” The second gives the reason why the person who is begotten by God is not able to sin (“because he has been begotten by God).”
(source)
I have many corroborating commentaries, btw.
Finally, I learned a long time ago not to contend for too long on FR with either unbelievers or trolls.