Just as I should not have to answer such a question on what the name of the seed in a believer is, you, and everyone should know that an act of sin is different from a state of sin.
This is an ideal to which every Christian is bound to aspire - inability to sin.
What John is saying here is that a Christian cannot persist in habitual, continual sin because he is born of God and the seed which which is of course the Lord Jesus Christ lives in him.
He cannot sin without a struggle or without a sense of grief so powerful that ultimately, despite his struggles, he will be brought to repentance and a forsaking of sin. What he is declaring to us, then, is that sin is no longer natural to the believer. Though, for a time, he may slip into it rather easily, nevertheless, it is now contrary to his nature. His heart is set toward God, and his life is a truceless antagonism against sin, and this must become apparent by breaking away from the bondage and slavery of sin.
"No one born of God commits sin; for God's nature abides in him," he declares and I believe!!! The child of God cannot persist, he cannot go on continuously living in what he knows to be sin.
If you will study the Greek grammer on this you will see that this is made clear in the tense of the compound verb, to commit sin. It is not aorist, which would have meant a single act of sin, but rather it is the present, continuous tense, "to go on committing sin."
In any case, Christ in us can never sin no matter how much we slice it up. Learning and understanding this person (Jesus Christ) in us is the key to sin not having it's way in a believer, which also has to do with the power given to a believer by God over it. All sin is linked to the devil.