The question has been asked, “What is the difference between the spirit of the law and the letter of the law?” To me, it all comes down to motivation.
When I stop at a red light to avoid getting a ticket, I am only obeying the letter of the law. Would I go ahead and run the red light and risk hurting someone if there was no risk of paying a fine? If so, then that doesn’t really make me an obedient person. It only makes me afraid of getting fined.
If I keep from running a red light because I don’t want to hit and hurt someone, then I am now obeying the spirit of the law, which is “others first” or “consideration for others.”
Here is one example of how the pharisees were looking at the letter of the law, while Jesus was looking at the spirit of the law.
At about that time Jesus was walking through some grainfields on the Sabbath. His disciples were hungry, so they began breaking off some heads of grain and eating them. But some Pharisees saw them do it and protested, “Look, your disciples are breaking the law by harvesting grain on the Sabbath.” Jesus said to them, “Haven’t you read in the Scriptures what David did when he and his companions were hungry? He went into the house of God, and he and his companions broke the law by eating the sacred loaves of bread that only the priests are allowed to eat. And haven’t you read in the law of Moses that the priests on duty in the Temple may work on the Sabbath? I tell you, there is one here who is even greater than the Temple! But you would not have condemned my innocent disciples if you knew the meaning of this Scripture: ‘I want you to show mercy, not offer sacrifices.’[ For the Son of Man is Lord, even over the Sabbath!” Matthew 12:1-8 NLT
First of all, I think the Pharisees were greatly exaggerating by calling taking a few heads of grain “harvesting”! Today some Sabbath keepers will not flip a light switch to avoid “starting a fire” on the Sabbath. But I do not think God was referring to light switches when He said, “don’t start a fire on the Sabbath.” See Exodus 35:3. back then a lot more work was involved in starting a fire than today. There is also a lot more involved in harvesting, than taking a few heads of grain. Now if you disagree with me, obviously that is fine. We all have our own convictions when it comes to these matters. For example, I do not eat out on the Sabbath because I do not want anyone to work for me on Sabbath (Exodus 20:10), and I do not want to buy and sell on Sabbath (Nehemiah 13:15-18). Some of my Sabbath-keeping friends do not see it that way, and do not consider the cooks or waitresses as their servants, and they consider Nehemiah was referring to a lot more work in loading and unloading food, than just serving it. Fine. Each to his or her own. We must all be convicted ourselves, but the motivation should always remain the same, which is love and consideration for God and others.
Second, Jesus refers to David eating the bread that was only for priests when he and his men were hungry. When you consider the fact that the law of God is love, then you can see how mercy here would be a higher priority than the letter of the law. Another example is in the story of the Good Samaritan. Many wonder if the priest and Levi thought the hurt man might be dead. If so they were not to touch him by law (See Leviticus 21:1-3 and Numbers 19:11-122). But even so, mercy always takes priority over the letter of the law. The law is love. If we put the letter of the law above love then we have just defeated the whole purpose of the law which is love.
Paul explains what it means to keep the Spirit of the law, which is love.
If you love your neighbor, you will fulfill the requirements of God’s law. For the commandments say, “You must not commit adultery. You must not murder. You must not steal. You must not covet.” These—and other such commandments—are summed up in this one commandment: “Love your neighbor as yourself.” Love does no wrong to others, so love fulfills the requirements of God’s law. Romans 13:8-10 NLT
Love does not do away with the commandments. It is because we love God and others that we keep the commandments. I can’t say I love my neighbor if I lie about her and steal from her. Love fulfills the Spirit of the law, which is love and consideration for God and others, while a sense of self preservation and selfishness fulfills only the letter of the law.