Now to say that we are born of Him is to say that we are children of God.  What a love is that which the Father has bestowed on us, that we should be called children!  Therefore the world knows us not, because it knew Him not. The apostle returns here to His appearing and its effect on us. We are children of God: this is our present sure and known position; we are born of God. That which we shall be is not yet manifested; but we know that--associated with Jesus as we are in the same relationship with the Father, Himself being our life-we shall be like Him when He appears. For it is to this we are predestined, to see Him as He now is with the Father, from which the life came which was manifested in Him and imparted to us, and to appear in the same glory.
Having then the hope of seeing Him as He is, and knowing that I shall be perfectly like Him when He appears, I seek to be as like Him now as possible, since I already possess this life-He being in me, my life.
This is the measure of our practical purification. We are not pure as He is pure; but we take Christ, as He is in heaven, for the pattern and measure of our purification, we purify ourselves according to His purity, knowing that we shall be perfectly like Him when He is manifested. Before marking the contrast between the principles of the divine life and of the enemy, he sets before us the true measure of purity (he will give that of love in a moment) for the children, inasmuch as they are partakers of His nature and have the same relationship with God.
There are two remarks to be made here. First, "hope in him" does not mean in the believer; but a hope that has Christ for its object. Second, it is striking to see the way in which the apostle appears to confound God and Christ together in this epistle; and uses the word "Him" to signify Christ, when he had just been speaking of God, and vice versa. We may see the principle of this at the end of chapter 5: "We are in him that is true, [that is to say] in his Son Jesus Christ. He is the true God and eternal life." In these few words we have the key to the epistle: Christ is the life. It is evidently the Son; but it is God Himself who is manifested, and the perfection of His nature, which is the source of life to us also, as that life was found in Christ as man. Thus I can speak of God and say, "Born of him;" but it is in Jesus that God was manifested, and from Him that I derive life; so that "Jesus Christ" and "God" are interchanged with each other. Thus "He shall appear" (chap. 2:28) is Christ, He is righteous; the righteous one "is born of him" But in chapter 3:1 it is " born of God," "children of God;" but the world did not know Him: here it is Christ on earth; and "when he shall appear," it is again Christ and we purify ourselves "even as He is pure." There are many other examples.
It is said of the believer, "he purifies himself:" this shews that he is not pure, as Christ is. He needed not to purify Himself. Accordingly it is not said, he is pure as Christ is pure (for in that case there would be no sin in us); but he purifies himself according to the purity of Christ as He is in heaven, having the same life as the life of Christ Himself.
Having set forth the positive aspect of christian purity, he goes on to speak of it in other points of view, as one of the characteristic proofs of the life of God in the soul.
He who commits sin (not transgresses the law,  but acts lawlessly. His conduct is without the restraint, without the rule of law. He acts without curb; for sin is the acting without the curb of law or restraint of another's authority, acting from our own will. Christ came to do His Father's will, not His own. But Christ was manifested that He might take away our sins, and in Him there is no sin; so that he who commits sin acts against the object of the manifestation of Christ, and in opposition to the nature of which, if Christ is our life, we are partakers. Therefore he who abides in Christ does not practise sin; he who sins has neither seen Him nor known Him. All depends, we see, on participation in the life and nature of Christ. Let us not then deceive ourselves. He who practises righteousness is righteous, as He is righteous: for, by partaking in the life of Christ, one is before God according to the perfection of Him who is there, the head and source of that life. But we are thus as Christ before God, because He Himself is really our life. Our actual life is not the measure of our acceptance; it is Christ who is so. But Christ is our life, if we are accepted according to His excellence; for it is as living of His life that we participate in this.
But the judgment is more than negative. He who practises sin is of the devil, has morally the same nature as the devil; for he sinneth from the beginning: it is his original character as the devil. Now Christ was manifested that He might destroy the works of the devil; how then can one who shares the character of this enemy of souls be with Christ?
On the other hand, he who is born of God does not practise sin. The reason is evident; he is made a partaker of the nature of God; he derives his life from Him. This principle of divine life is in him. the seed of God remains in him; he cannot sin, because he is born of God. This new nature had not in it the principle of sin, so as to commit it. How could it be that the divine nature should sin?
Having thus designated the two families, the family of God and that of the devil, the apostle adds the second mark, the absence of which is a proof that one is not of God. He had already spoken of righteousness; he adds the love of the brethren. For this is the message that they had received from Christ Himself, that they should love one another. In verse 12 he shews the connection between the two things: that hatred of a brother is fed by the sense one has that his works are good, and one's own evil. Moreover we are not to wonder that the world hates us: for we know that we have passed from death unto life, because we love the brethren. If this love is an essential proof of being renewed, it is quite natural that it should not be found in the men of the world.
But, this being the case, he who does not love his brother (solemn thought!) abides in death. In addition to this, he who does not love his brother is a murderer, and a murderer has not eternal life. There is the absence of the divine nature, death; but more, the activity of the old man in the opposite nature is there, he hates, and is in spirit the activity of death-a murderer.
Further, as in the case of righteousness and of purity, we have Christ as the measure of this love. We know love by this, that He laid down His life for us; we ought to lay down ours for the brethren. Now, if our brother has need, and we possess this world's good, but do not provide for his necessity, is that the divine love which made Christ lay down His life for us? It is by this real and practical love that we know we are in the truth, and that our heart is confirmed and assured before God. For if there is nothing on the conscience, we have confidence in His presence; but if our own heart condemns us, God knows yet more.
It is not here the means of being assured of our salvation, but of having confidence in the presence of God. We cannot have it with a bad conscience in the practical sense of the word, for God is always light and always holy.
We also receive all that we ask for, when we walk thus in love before Him, doing that which is pleasing in His sight; for thus walking in His presence with confidence, the heart and its desires respond to this blessed influence, being formed by the enjoyment of communion with Him in the light of His countenance. It is God who animates the heart; this life, and this divine nature, of which the epistle speaks, being in full activity and enlightened and moved by the divine presence in which it delights. Thus our requests are only for the accomplishment of desires that arise when this life, when our thoughts, are filled with the presence of God and with the communication of His nature. And He lends His power to the fulfillment of these desires, of which He is the source, and which are formed in the heart by the revelation of Himself. (Compare John 15:7)
This is indeed the position of Christ Himself when here below: only that He was perfect in it. (Compare John 8:29; 11:42)
And here it is the commandment of God which He desires us to obey; namely, to believe on the name of His Son Jesus; and to love one another, as He gave us commandment.
Now he who keeps His commandments dwells in Him; and He dwells also in this obedient man. It will be asked whether God or Christ is here meant? The apostle, as we have seen, confounds them together in his thought. That is to say, the Holy Ghost unites them in our minds. We are in Him who is true, that is, in His Son Jesus Christ. It is Christ, who is the presentation of God to men in life in man; and to the believer He is the communication of that life, so that God too dwells in him, in the revelation, in its divine excellence and perfection, of the nature which the believer shares in the power of the Holy Ghost who dwells in him, so that love is alike enjoyed and exercised.
But what marvelous grace to have received a life, a nature, by which we are enabled to enjoy God Himself, who dwells in us, and by which, since it is in Christ, we are in fact in the enjoyment of this communion, this relationship with God! He who has the Son has life; but God then dwells in him as the portion, as well as the source of this life; and he who has the Son has the Father.
What marvelous links of vital and living enjoyment through the communication of the divine nature of Him who is its source; and that according to its perfection in Christ! Such is the Christian according to grace. Therefore also he is obedient, because this life in the man Christ (and it is thus that it becomes ours) was obedience itself, the true relationship of man to God.
Practical righteousness, then, is a proof that we are born of Him who, in His nature, is its source. In presence also of the world's hatred, we know that we have passed from death unto life because we love the brethren. Thus, having a good conscience, we have confidence in God, and we receive from Him whatsoever we ask, walking in obedience and in a way that is pleasing to Him. Thus walking,  and He in us.
A third proof of our christian privileges arises here. The Spirit whom He has given us is the proof that He Himself dwells in us, the manifestation of the presence of God in us. He does not here add that we abide in Him, because the subject here is the manifestation of the presence of God. The presence of the Spirit demonstrates it. But in abiding in Him there is, as we shall see farther on, the enjoyment of that which He is, and consequently moral communion with His nature. He who obeys enjoys this also, as we have seen. Here the presence of the Holy Ghost in us is spoken of as demonstration of one part only of this truth, namely, that God is in us. But the presence of God in us according to grace, and according to the power of the Spirit, involves also communion with that nature; we dwell also in Him from whom we derive this grace, and all the spiritual forms of that nature, in communion and practical life. It is in verses 12 and 16 of chapter 4. that our apostle speaks of this.
Practical righteousness or obedience, the love of the brethren, the manifestation of the Spirit of God, are the proofs of our relationship to God. He who obeys the Lord's commandments in practical righteousness dwells in Him, and He in him. The Spirit given is the proof that He dwells in us.