Brotherly love is the effect of the new birth, which makes obedience to all God's commandments pleasant. (1-5) Reference to witnesses agreeing to prove that Jesus, the Son of God, is the true Messiah. (6-8) The satisfaction the believer has about Christ, and eternal life through him. (9-12) The assurance of God's hearing and answering prayer. (13-17) The happy condition of true believers, and a charge to renounce all idolatry. (18-21)1-5 True love for the people of God, may be distinguished from natural kindness or party attachments, by its being united with the love of God, and obedience to his commands. The same Holy Spirit that taught the love, will have taught obedience also; and that man cannot truly love the children of God, who, by habit, commits sin or neglects known duty. As God's commands are holy, just, and good rules of liberty and happiness, so those who are born of God and love him, do not count them grievous, but lament that they cannot serve him more perfectly. Self-denial is required, but true Christians have a principle which carries them above all hinderances. Though the conflict often is sharp, and the regenerate may be cast down, yet he will rise up and renew his combat with resolution. But all, except believers in Christ, are enslaved in some respect or other, to the customs, opinions, or interests of the world. Faith is the cause of victory, the means, the instrument, the spiritual armour by which we overcome. In and by faith we cleave to Christ, in contempt of, and in opposition to the world. Faith sanctifies the heart, and purifies it from those sensual lusts by which the world obtains sway and dominion over souls. It has the indwelling Spirit of grace, which is greater than he who dwells in the world. The real Christian overcomes the world by faith; he sees, in and by the life and conduct of the Lord Jesus on earth, that this world is to be renounced and overcome. He cannot be satisfied with this world, but looks beyond it, and is still tending, striving, and pressing toward heaven. We must all, after Christ's example, overcome the world, or it will overcome us to our ruin.

6-8 We are inwardly and outwardly defiled; inwardly, by the power and pollution of sin in our nature. For our cleansing there is in and by Christ Jesus, the washing of regeneration and the renewing of the Holy Ghost. Some think that the two sacraments are here meant: baptism with water, as the outward sign of regeneration, and purifying from the pollution of sin by the Holy Spirit; and the Lord's supper, as the outward sign of the shedding Christ's blood, and the receiving him by faith for pardon and justification. Both these ways of cleansing were represented in the old ceremonial sacrifices and cleansings. This water and blood include all that is necessary to our salvation. By the water, our souls are washed and purified for heaven and the habitation of saints in light. By the blood, we are justified, reconciled, and presented righteous to God. By the blood, the curse of the law being satisfied, the purifying Spirit is obtained for the internal cleansing of our natures. The water, as well as the blood, came out of the side of the sacrificed Redeemer. He loved the church, and gave himself for it, that he might sanctify and cleanse it with the washing of water by the word; that he might present it to himself a glorious church, #Eph 5:25-27|. This was done in and by the Spirit of God, according to the Saviour's declaration. He is the Spirit of God, and cannot lie. Three had borne witness to these doctrines concerning the person and the salvation of Christ. The Father, repeatedly, by a voice from heaven declared that Jesus was his beloved Son. The Word declared that He and the Father were One, and that whoever had seen him had seen the Father. And the Holy Ghost, who descended from heaven and rested on Christ at his baptism; who had borne witness to Him by all the prophets; and gave testimony to his resurrection and mediatorial office, by the gift of miraculous powers to the apostles. But whether this passage be cited or not, the doctrine of the Trinity in Unity stands equally firm and certain. To the doctrine taught by the apostles, respecting the person and salvation of Christ, there were three testimonies. 1. The Holy Spirit. We come into the world with a corrupt, carnal disposition, which is enmity to God. This being done away by the regeneration and new-creating of souls by the Holy Spirit, is a testimony to the Saviour. 2. The water: this sets forth the Saviour's purity and purifying power. The actual and active purity and holiness of his disciples are represented by baptism. 3. The blood which he shed: and this was our ransom, this testifies for Jesus Christ; it sealed up and finished the sacrifices of the Old Testament. The benefits procured by his blood, prove that he is the Saviour of the world. No wonder if he that rejects this evidence is judged a blasphemer of the Spirit of God. These three witnesses are for one and the same purpose; they agree in one and the same thing.

9-12 Nothing can be more absurd than the conduct of those who doubt as to the truth of Christianity, while in the common affairs of life they do not hesitate to proceed on human testimony, and would deem any one out of his senses who declined to do so. The real Christian has seen his guilt and misery, and his need of such a Saviour. He has seen the suitableness of such a Saviour to all his spiritual wants and circumstances. He has found and felt the power of the word and doctrine of Christ, humbling, healing, quickening, and comforting his soul. He has a new disposition, and new delights, and is not the man that he formerly was. Yet he finds still a conflict with himself, with sin, with the flesh, the world, and wicked powers. But he finds such strength from faith in Christ, that he can overcome the world, and travel on towards a better. Such assurance has the gospel believer: he has a witness in himself, which puts the matter out of doubt with him, except in hours of darkness or conflict; but he cannot be argued out of his belief in the leading truths of the gospel. Here is what makes the unbeliever's sin so awful; the sin of unbelief. He gives God the lie; because he believes not the record that God gave of his Son. It is in vain for a man to plead that he believes the testimony of God in other things, while he rejects it in this. He that refuses to trust and honour Christ as the Son of God, who disdains to submit to his teaching as Prophet, to rely on his atonement and intercession as High Priest, or to obey him as King, is dead in sin, under condemnation; nor will any outward morality, learning, forms, notions, or confidences avail him.

13-17 Upon all this evidence, it is but right that we believe on the name of the Son of God. Believers have eternal life in the covenant of the gospel. Then let us thankfully receive the record of Scripture. Always abounding in the work of the Lord, knowing that our labour is not in vain in the Lord. The Lord Christ invites us to come to him in all circumstances, with our supplications and requests, notwithstanding the sin that besets us. Our prayers must always be offered in submission to the will of God. In some things they are speedily answered; in others they are granted in the best manner, though not as requested. We ought to pray for others, as well as for ourselves. There are sins that war against spiritual life in the soul, and the life above. We cannot pray that the sins of the impenitent and unbelieving should, while they are such, be forgiven them; or that mercy, which supposes the forgiveness of sins, should be granted to them, while they wilfully continue such. But we may pray for their repentance, for their being enriched with faith in Christ, and thereupon for all other saving mercies. We should pray for others, as well as for ourselves, beseeching the Lord to pardon and recover the fallen, as well as to relieve the tempted and afflicted. And let us be truly thankful that no sin, of which any one truly repents, is unto death.

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.

Commentary by Matthew Henry, 1710.