5:18 {17} We know that whosoever is born of God sinneth not; but he that is begotten of God keepeth himself, and that wicked one toucheth him not.
(17) A reason why not all, or rather why no sin is mortal to some: that is, because they are born of God, that is to say, made the sons of God in Christ, and being ended with his Spirit, they do not serve sin, nor are they mortally wounded by Satan.
5:18 Whosoever is born of God sinneth not. Does not live a life of sin. He will not sin unto death, though he may be overtaken in a fault. See PNT 1Joh 5:21.
That wicked one toucheth him not. Cannot lay hands on him so as to hold him.
5:18 Yet this gives us no encouragement to sin: on the contrary, it is an indisputable truth, he that is born of God - That sees and loves God. Sinneth not - So long as that loving faith abides in him, he neither speaks nor does anything which God hath forbidden. He keepeth himself - Watching unto prayer. And, while he does this, the wicked one toucheth him not - So as to hurt him.
5:18-21 All mankind are divided into two parties or dominions; that which belongs to God, and that which belongs to the wicked one. True believers belong to God: they are of God, and from him, and to him, and for him; while the rest, by far the greater number, are in the power of the wicked one; they do his works, and support his cause. This general declaration includes all unbelievers, whatever their profession, station, or situation, or by whatever name they may be called. The Son leads believers to the Father, and they are in the love and favour of both; in union with both, by the indwelling and working of the Holy Spirit. Happy are those to whom it is given to know that the Son of God is come, and to have a heart to trust in and rely on him that is true! May this be our privilege; we shall thus be kept from all idols and false doctrines, and from the idolatrous love of worldly objects, and be kept by the power of God, through faith, unto eternal salvation. To this living and true God, be glory and dominion for ever and ever. Amen.
