Throughout the New Testament we can read about love, and how important it is to love one another. Throughout his entire ministry on earth, Jesus emphasized that as he loved us, we should love one another. It was so important that he said it was a new commandment for us. We read this everywhere in the Gospels and in the Epistles, and in Revelation. Love is the most fundamental thing in God. Jesus loved God and he gave his life in love for us. Jesus taught us to love one another and to be each other’s servants.
“Teacher, which commandment is the greatest in the law?” He answered, “‘You shall love the Lord your God with all your heart and with all your soul and with all your mind.’ This is the greatest and first commandment. And the second is as great as this: ‘You shall love your neighbor as yourself.’ On these two commandments hang all the Law and the Prophets.” (Matthew 22:36-40)
“A new commandment I give to you, that you love one another. Just as I have loved you, you also must love one another. By this everyone will know that you are my disciples, if you love one another.” (John 13:34-35)
Let love be genuine! Abhor what is evil and cling to what is good. Love one another with sincere brotherly affection; esteem others more than yourselves. (Romans 10:9-10)
Finally, be like-minded, show compassion, love one another as brothers, be compassionate and humble. Do not repay evil for evil or insult for insult. On the contrary, bless, for you were called to inherit a blessing. (1 Peter 3:8-9)
And this is his commandment: that we believe in the name of his Son Jesus Christ, and love one another, as he commanded us. (1 John 3:23)
In the Old Testament, the sum of the law and the prophets is to love God with all our heart and with all our understanding and with all our strength. And in this way, the purpose is exactly the same in both the old covenant and the new covenant. We are to be each other's servants, love Jesus, love God, believe for salvation. In the New Covenant, God will write the law in our hearts. That is what is meant by Jesus coming to fulfill the law: He set the standard of loving the Father and being each other's servants, in love. That is what God wants, servants who will worship him in spirit and truth.
That is what is at the basis of marriage too: a man and a woman coming together and living together in love. In this stable framework, we have children in love, and parents love their children. It is in the same way that God loves us, and calls us his children, even heirs. Jesus made this clear when he called the children to himself and said that the kingdom of God belongs to such. The Father wants us to come to him in childlike trust, so that he can show his fatherly heart to us, his children. Because of love, we have children with God.
Jesus himself uses the image of the bride and groom, as a picture of the love between Jesus and his church. So in both covenants the main message is that we should love God and love each other. That is the greatest thing, and the whole purpose of both the old and the new covenant, albeit in two completely different ways. In the old covenant, the Israelites had to finally capitulate and recognize that no one can keep the law, and come to God and ask for mercy and forgiveness. God would then forgive and be their God.
Paul says that gifts of grace will end, but love will never end, neither in this world nor in the world to come. Therefore, it is greater to love one another than to have the other gifts of grace. Living in love is absolutely fundamental, and if one does not do it, it is a sign that something is wrong. Whoever does not love his neighbor, but does wrong, is not known by Jesus (Luke 13:27 and 1 John 4:8). This is because the fruit of the spirit is love, joy and peace. So love is the fulfillment of the law, the prophets and the new covenant.