The law was and is the school-master, ever pointing us to Christ. Legalism mistakes the classroom for graduation. Gentile legalists have taken the law and made it the end instead of the means. They live life, figuratively speaking, chanting their long and short vowel sounds, drilling their math facts, strutting their Geometry theorems...thinking that the Greatest Teacher of All is giving them a straight "A".
When the point of the law was to point us to the One who is not a ordinance, is not a law, is not a rule, but is a person.
The difference between living under the law and living under grace is the difference between being in school all your life, making straight A's...
...and graduating, falling in love, starting a family, and nurturing that family by all means possible. Legalist believers and Grace believers know the same things and do some of the same things - but only the Grace believer , who truly understands grace, is able to take what she knows and apply it to her relationships. Only the grace believer does what she does for the higher and deeper and better reason. Because of relationship.
And relationships are all that matter - loving God and loving the people He has placed in proximity to us in this life.