Hey Shnarkle, I guess if He’s written it on our heart there’s no need to read the letter?
It's still good to have an understanding of God's will as well as confirming what's in our heart agrees with the witness of saints. The letter provides a baseline; the Spirit allows the heart to manifest the letter in every situation we find ourselves in. This is what we see in the gospels.
The law informs us to never look back or even return for the gleanings of the harvest. Jesus says we aren't fit for the kingdom even if we look back from the plow.
Some think we needn't concern ourselves with tithing mint and cumin, but Christ's parables point out that if we can handle the little things in the kingdom we will be given greater responsibilities as well; i.e. the "weightier matters of the law". if we can't be bothered to tithe mint and cumin, we're not going to be able to handle anything more than that.
The law stipulates we must repay the value of an eye for an eye, the value of a tooth for a tooth, but Christ says if we're sued for our coat, we must give them our shirt as well. if we're compelled into service for one mile, we will go another as well.
Self sacrifice allows one the freedom to give freely from God's endless surplus. It is only when we hold onto ourselves that we are locked into bondage, and can only do for others what we should rather than what overflows from God's love.