The key is in verse 16: "...he that dwelleth in love dwelleth in God, and God in him." God dwells in the believer through the Holy Spirit. According to Galatians 5:22, the first attribute of the fruit of the spirit is love. Now, I believe that we, in and of ourselves, are capable of a degree of love without the filling of the Holy Spirit. Even an unsaved person can love to a degree. But this list of attributes in Galatians 5:22 is only available to the Christian who is filled with the Spirit. But if we are capable of loving without the Holy Spirit, then why is love listed as an attribute that only comes from the Holy Spirit? I believe the answer lies within the fact that there is a degree of love that can only come from the Spirit of God. While we may be able to love to a limited degree, it is the filling of the Holy Spirit that allows us to love beyond those limits, thus giving us perfect love. While we may be able to love our family, it is the filling of the Holy Spirit that allows us to love our enemies.
Romans 5:5 supports this thought. "And hope maketh not ashamed; because the love of God is shed abroad in our hearts by the Holy Ghost which is given unto us." It is amazing that when we are filled with the Spirit, we have access to the same love that God had when He sent His only begotten Son to the cross.
It was this perfect love that allowed Elisabeth Elliot (whom we named out daughter after) to return to the very men that slaughtered her husband and lead them to Christ. And it is this perfect love that we need each moment of each day.