During a discussion with an officer of The Salvation Army he remarked that the two Great Commandments attributed to Jesus in the synoptic gospels were simple, yet profound. Add the Golden Rule and you have in a nutshell a theology of helping people at point of need and campaigning for social justice, all done in love. Academics label this theology 'progressive', adding love and care for all creation to its attributes.
Variants on the theme of progressive theology include liberation, feminist, black and other equality theologies, each stemming from the injunction to love your neighbour.
Some define their belief/faith as being encompassed by Matthew 25 which rather limits the scope of progressive theology, but illustrates an important point. A broad, sweeping principle is open to interpretations seeking to either limit or expand its application.
Detailed rules are more cut and dried in application. It is important to distinguish a system only permitting actions contained within the rules from those permitting actions where the rules are silent.
Principles are applied flexibly and are susceptibe to novel interpretation, rules are applied rigidly unless a degree of flexibilty is contained within them.