... purifying of your soul in the obedience to the truth, to the extent a sincere brotherly love, agape love for one another, fervently from a pure heart (1 Peter 1:22)
Owe no one anything, except to love each other, for the one who loves another has fulfilled the law. For the commandments, “You shall not commit adultery, You shall not murder, You shall not steal, You shall not covet,” and any other commandment, are summed up in this word: “You shall love your neighbor as yourself.” Love does no wrong to a neighbor; therefore love is the fulfillment of the law (Romans 13:8-10)Loving your brother Jesus said is like the first great commandment to love God (Matthew 22:37-39). He did not say loving your brother was the second great commandment but he said it was like the great commandment as loving God in purity of heart produces a sincere love for one another. Thus Jesus like Paul in the above verse equates loving God and loving your brother as the fulfillment of the law or commandments.
If we think about the ten commandments, you see love; love God and love your neighbor. Love God; don't worship other gods or idols, don't take his name in vain, set aside a day to remember him. Love your brother; don't murder him, sleep with his wife, steal from him, or covet his wife or things. The simplicity of obedience is seen in agape and brotherly love. But this is where our hearts are challenged. For even if we say love is our motivation to correct others in their disobedience, if it doesn't flow from love we can wrong a brother, cause a brother to stumble in their faith.
Jesus said in the end times because of persecution and sin and false prophets leading people astray, many will fall away and betray one another and hate one another and "the agape love of many will grow cold" (Matthew 24:7-14). There will be a religious system, as there will be many false prophets, but it will lack love. Jesus equates obedience with loving one another. John writes we know we are children of God because we love his children (1 John 5:1-6). If we do not love we walk in darkness and do not walk as Jesus.
Jesus said if you love me then obey my commandments then he gives what is called the new commandment to love one another as he loves. John writes, we know we love God if we keep his commandments. We can keep many commandments and do many religious activities and think we are in right standing with God. But the scriptures are very clear, if we do not love one another we walk in darkness and the truth is not abiding in us (1 John 2:3-11). This lack of love the scriptures equates to being disobedient. If we love him we will obey his command and he commanded us to love one another.
A beautiful thing about the new covenant is Jesus continues working in us and for us, he is our advocate before the Father (1 John 2:1-2). So if we do walk in darkness, which is equated to the sin of not loving our brother, and causing him to stumble (1 John 2:8-11) we can confess our sin and be cleansed from all unrighteousness (1 John 1:5-10).
Peter writes grace and peace increase in knowledge of Jesus (2 Peter 1:2). Then he writes there are qualities that we add to our faith and if we do and are increasing in them we will be effective and productive in knowing Jesus (2 Peter 1:5-8). Adding to faith virtue and knowledge will produce a life that reigns in Christ, through endurance into godliness, and this godliness, purity of heart, produces brotherly and agape love.
Serving one another in sincere fervent love is a sign of our maturity, that we do not use our freedom as a means to give into fleshly desires (Galatians 5:13). Paul prays that love will abound more and more in knowledge and discernment so that we can prove what is essential so that we exist pure and without blame filled with fruit of righteousness (Philippians 1:9-11). He also prays we are rooted and founded in love so that we have strength to lay hold of a greater love of God, so to be filled to the fullness of God (Ephesians 3:14-20). I take fullness to be maturity, walking like Christ, and love plays an important role. It is not fear that will keep us obedient and bring us into maturity, but it is love (1 John 4:18; Luke 1:74,75; Romans 8:15; 2 Timothy 1:7). And this is what it means when the scriptures say the love of God is fulfilled in us when we obey his commands, by loving one another (1 John 4:12) maturely walking like Jesus did in this world (1 John 4:18). Faith and love will bring us into maturity.
Blessed are the pure in heart, for they shall see God (Matthew 5:8)When we purify our soul in the obedience to the truth, the outcome is a sincere brotherly love, agape love for one another, fervently from a pure heart (1 Peter 1:22). By this pure love for one another the world will know we are his disciples. Thus we can equate purity of heart to loving one another and to obedience or said another way those who love his brethren are pure in heart and will see God. Jesus said, "in as much as you have done it unto one of the least of these my brethren, you have done it unto me" (Matthew 25:37–40).