Many of the countries, companies, religious orders and associations have a charism or a founding principles or a focus. These take the form of constitutions or rule books or manuals. The latter is created for the sake of former. In sociology, we speak of the need and danger of the institutionalization of a experience or an idea or a pioneering initiative. Here institutions are at the service of the original experience. Even all the religions of the world are institutionalization of the a foundational experience of a person (Jesus or Buddha or Mohammed).
Many a times the unwritten rule of service to charism by the institution is forgotten and institution takes the role of master. The rules become sacrosanct, which could be modified by none. In the gospels, Jesus questions the pharisees who in the name of interpretation makes extra rules which makes life burdensome, which forget the original charism. Pope Francis in his attempts to show that God is a loving and merciful father is trying to do the same thing; to revive that image of God which is present in the Christian theology and spirituality, but forgotten in the name of other nitty grities.
In the post-modern world and philosophy, the word letter than the spirit makes a lot of sense. Post-modernity as an attitude is not that anything can go about, but that alternate interpretations are possible according to the context.
We have judges in the courts, and the courts follow the basic laws of our country. But they also interpret it. If they are blindly follow the laws, it is better to replace them with machines. Derrida would say that any decision should be undecidable. We don’t have full set of knowledge about that case (we are not almighty to know everything) and there is urgency to take a decision. So we are in a dilemma, but we should take the decision. Judge is appointed to take the decision keeping in mind the spirit of law than the letter of law. (I visualize law system like this…. I agree it has its own dangers).
Religious Fundamentalism and false notions of nationalism are based on the laws, rather than looking at the spirit of the holy books or constitutions or some ideologies. A simple hypothetical example could be like this. A king made a decision that cutting of a particular tree in a forest was banned for 25 years as they were nearing extinction. Though people murmured in the beginning, it became a sacred rule for them. After 40 years, there was a huge number of trees in the forest; they were growing like weeds; they were affecting the bio-diversity of the forest. Some wise man suggested that we should chop down some of these type of trees and plant some variety. A mob got angry and killed the wise man.
Be blind followers or imitators of the letters of law,
but be companions of the spirit of the law.