The Pharisees

The Letter of the Law is not a bad thing.  After all, it was given to us by God. The Letter of the Law is holy, good, and spiritual, but imperfect (CCC 1963; Romans 7:12, 14, 16). We have the laws such as the Ten Commandments to guide us, and these laws (with the exception of the Jewish Sabbath) were never abolished.  The Letter of the Law shows what must be done, but does not of itself give the strength, the grace of the Spirit, to fulfill it (CCC 1963)  

In the Holy Bible, we see Christ often condemning the Pharisees of using the Letter of the Law to avoid the higher obligation.  An example of this is when the Pharisees condemned Christ and His disciples for plucking grain and eating it on the Sabbath because they were hungry (Mark 2:23). 

The Pharisees followed the Letter of the Law, which forbids work.  The Old Testament does say that one is forbidden to do all kinds of work (Deuteronomy 5:14).  In fact, a man who was gathering sticks on the Sabbath was put to death (Deuteronomy 15:32-36).  So, the Pharisees were following the Letter of the Law.  In this case, the Pharisees saw it more lawful and better to allow a brother to go hungry because obedience to the law was more important than feeding the brother.  Christ's response to this was "Sabbath was made for man, not man for the Sabbath."

Following the Spirit of the Law is not a means to avoiding the Letter of the Law.  It is a means of understanding what the real purpose of the Law is, and keeping the Letter of the Law in the context of the two greatest commandments, which is to love God with your whole heart, mind, and soul and to love your neighbor as yourself.  

Christ also condemned the Pharisees for hypocrisy.  The Pharisees were very knowledgeable in the Letter of the Law, but they lack the Spirit of the Law. There are also some Catholics who are like the Pharisees.  They know the Letter of the Law very well and follow it completely, but they lack the Spirit of the Law.