I'm not sure there is a difference between the perfect/royal law?
He is referring to "love your neighbor as yourself" and "Love the lord your God with all your heart, mind and soul".
This law frees us from having to worry about a list of do's and don'ts...If we truly are focusing on the "perfect law", we will still be following all of God's commands, but not out of fear, or because we are trying to meet a list of requirements, but because we have been forever changed and forever freed from sin. We now obey His law through the power of His grace, the outpouring of His love within us...
It is probably only in the past year or so that I have really realized the liberty that life in Christ gives. It is hard for me to express it, but I finally know I am free, a slave to sin no more. Christians sometimes get so bogged down in things like the length of women's skirts, whether to go to Disney movies, what kind of music is acceptable...I think that lately I am really impatient with such discussions. If I am truly free, if I am a new creation, then suddenly I'm not driven by how long my hem should be, or what my radio dial is tuned to. Because I am a child of Christ, I will now by his grace act and think differently. The same music I used to tolerate as "not that bad" is suddenly offensive and no longer something I want in my life. It's not that I don't listen to it because it is "bad", it is because I am free from that way of thinking, the mindset in those songs. Now I hear the lyrics and think, "If you only knew the real Answer!".