1 John 3:8 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.
"comitteth sin" - "doing the sin", "practicing the sin".
doing, practicing - this is a present participle and can indicate a state of being "sinneth from the beginning".
The use of the definite article (which does not show up in the English) "The" sin along with the present participle indicates sin as a way of life.
Anyone who sins in this manner is not saved
It does not say "He who sins is of the devil", (as present active) this is called "present active" or punctiliar sins, one at a time and not continuously.
These "present active" sins are covered in 1 John 1:9
1 John 1:9 If we confess our sins (plural), he is faithful and just to forgive us our sins, and to cleanse us from all unrighteousness.
"If we confess our sins" as oppossed to "He that committeth sin"
Those who are "practicing" sin are in the state of sin, they can't identify their sins (plural) because their whole life is a sin every moment and they belong to their father the devil. If they die in that condition as slaves to sin then they will die in their sin.
The children of God cannot sin in this manner because we are born of God and belong to our Father in heaven and the Spirit (the seed of the rebirth) remains within us us and convicts us to acknowledge our individual sins.
There is a possible consequence for obstinant unrepentant sinning on the part of a child of God - physical death - the sin unto death.
Paul also speaks of this:
1 Corinthians 1
29 For he that eateth and drinketh unworthily, eateth and drinketh damnation to himself, not discerning the Lord's body.
30 For this cause many are weak and sickly among you, and many sleep.
31 For if we would judge ourselves, we should not be judged.
32 But when we are judged, we are chastened of the Lord, that we should not be condemned with the world.
Verses 31 shows that even this condition can be remitted by the Lord, our heavenly "Lawyer":
As well as:
1 John 2:1 My little children, these things write I unto you, that ye sin not. And if any man sin, we have an advocate (lawyer) with the Father, Jesus Christ the righteous:
However, we are admonished by our loving Father in heaven in the first part of this verse:
1 John 2:1 My little children, these things write I unto you, that ye sin not...
See, it is really our Father in heaven who asks us not to sin but nevertheless has provided us a means to maintain our fellowship of love with Him and we want to do so because we love Him who first loved us.
As Winman has witnessed, we hate our sin.
Look to that atoning fountain of blood drawn from His veins and you won't have to worry about whether He is Lord of your life or not.
HE IS.
HankD