In Galatians chapter 5, Paul is talking about the Law of Moses, which was given by God to Israel. A law whose very foundation is love. Because love is the basis for all that God does, and it should be the same for us. For how can we say we love God, and not love those He calls His. If the Holy Spirit truly lives in our hearts, love should flow easily from us towards others. And loving our neighbors as we love ourselves is a natural response when our love for God allows us to see them as He does, our fellow brothers and sisters in Christ.