"The New Law is chiefly the grace itself of the Holy Spirit"

"NOW that which is preponderant in the law of the New Testament, and whereon all its efficacy is based, is the grace of the Holy Spirit, which is given through faith in Christ. Consequently the New Law is chiefly the grace itself of the Holy Spirit, which is given to those who believe in Christ."

~St. Thomas Aquinas: Summa Theologiae, I-II, Q. 106, Art. 1.