Here he is highlighting the importance of extending love to one another. He is saying: if at all you owe anything, it must be love towards one another. 

The first of Ten Commandment explains how we are to love God. The latter ones explain what we should do and what we should not do so as to extend love to fellow brethren.

But Jesus summarized all the lows into one and gave that as a command: Love one another. This love He has exhibited by offering His own life for the one He loved, or said He loved. In the same way we have to one another. It is not enough we say we love; it has to felt by the person to whom we are extending our love.

For he loves another has fulfilled the law.
There are so many laws that are present in the Bible, but the one who fulfills this law fulfills the entire law. Imagine the importance that He is giving.

God loves us generously, and from His love we know what does it mean to be love or t love. Let us realize God's love, let us realize Jesus' love, let us realize the Holy Spirit' love. From This love, from our heart let love generate and flow towards persons who are living around us; many of them who are really in need of love. If at all there is something that the world needs now, right now it is love. You and I should be agents of love to the persons who are in need of that, thereby fulfilling the Law.

Abba, Thank You for loving us this generously. We worship Your Son who is the embodiment of Your Total Love. Let Your Spirit lead us that we may be able to love each and everyone who deserves our love.