I don't think that to act in the spirit of the law is to disregard the law, to ignore the law, to dispense one's self from the law, or even to dispense others from it. Of course, when it comes to living our Christian faith, it certainly does not mean imposing it on others, or even imagining that it is imposed on ourselves from the outside. It is proposed to us and we, in turn, once we have accepted the proposal, propose it to others. Living the law of Christ, according to the Spirit, means concerning ourselves first and foremost with our own obedience and not that of others.
In Sacred Scripture St. Paul mentions "spirit" and "letter" in 2 Corinthians 3:6. To locate his words in their context, he is writing about his call to be an apostle, noting first that he was called according to the spirit, not according to the letter, before noting that the letter kills, but "the Spirit gives life."
One way to summarize what he goes on to write is by pointing out that if one wants to see how to observe the law according to the Spirit, one needs to look to Jesus. We look to Jesus precisely because of the perfect way He not only obeyed, but, through His perfect obedience, fulfilled the law. Continuing, the apostle notes that "if the ministry of death, carved in letters on stone, was so glorious that the Israelites could not look intently at the face of Moses because of its glory that was going to fade, how much more will the ministry of the Spirit be glorious?" (2 Cor. 3:7-8) The reason Paul refers to the law given to Moses as "the ministry of death" is not because the law was defective. No! As Jesus showed so luminously, the defect is in us!
For what the law, weakened by the flesh, was powerless to do, this God has done: by sending his own Son in the likeness of sinful flesh and for the sake of sin, he condemned sin in the flesh (Rom. 8:3)In the first instance, living the Spirit of the law requires discerning why it was promulgated. Then it has to do with my intention, with why I obey it. The answer to both questions is love. Obeying out of love is the only way for my righteousness to exceed "that of the scribes and Pharisees" (Matt. 5:20). This why Jesus taught- "You shall love the Lord, your God, with all your heart, with all your soul, and with all your mind. This is the greatest and the first commandment. The second is like it: You shall love your neighbor as yourself. The whole law and the prophets depend on these two commandments" (Matt. 22:37-40).