1 John 3:8

He that committeth sin is of the devil
Not everyone that sins, or commits acts of sin, then every man is of the devil, because no man lives without the commission of sin; but he who makes sin his constant business, and the employment of his life, whose life is a continued series of sinning, he is of the devil; not as to origin and substance, or by proper generation, as some have literally understood the words; but by imitation, being like him, and so of him their father, doing his lusts, living continually in sin, as he does, and so resemble him, as children do their parents; and hereby also appear to be under his government and influence, to be led captive by him at his will, and so to belong to him, and such as will have their part and portion with him in the lake which burns with fire and brimstone, so living and dying:

for the devil sinneth from the beginning;
not of his creation, for he was made by God a pure and holy creature; but from the beginning of the world, or near it, at least from the beginning of man's creation; for he not only sinned by rebelling against God himself, and by drawing in the rest of the apostate angels into the rebellion with him, but by tempting man, as soon as created, to sin against God: what was his first and particular sin is not certain, whether pride or envy, or what; seems to be, his not abiding in the truth, or an opposition to the truth of the Gospel, respecting the incarnation of the Son of God, mentioned in the following clause; see ( John 8:44 ) ; however, he has been continually sinning ever since: he "sinneth"; he is always sinning, doing nothing else but sin; so that he that lives a vicious course of life is like him, and manifestly of him:

for this purpose the Son of God was manifested;
in human nature, as in ( 1 John 3:5 ) ; whence it appears that he was the Son of God before his incarnation, and so not by it; he did not become so through it, nor was he denominated such on account of it; he was not made the Son of God by it, but was manifested in it what he was before; and for this end:

that he might destroy the works of the devil;
and the devil himself, and all his dominion and power, and particularly his power over death, and death itself; and especially the sins of men, which are the works of the devil, which he puts them upon, influences them to do, and takes delight in; and which are destroyed by Christ, by his sacrifice and death, being taken, carried, removed away, finished, and made an end of by him; (See Gill on 1 John 3:5).