《神學大全》中的恩寵與法律，其主要論述的即是關於實踐哲學方面的課題開始，進而談論到神學的根源天主！所以，本著作不僅是一本哲學著作，更是一本有神學的巨作。論述到法律的部份，大師的主要目的是透過論述，然後深化信仰實質上的內容。藉著對法律多元面的討論，來探討其普世的基礎－永恆的法律。其內容包含了永恆法律、自然律、人律、新約中的法律及舊約中的法律。而大師也一再強調，法律固然重要，人的本性若沒有恩寵的助佑，或說人若不善用來自天主的恩寵，人無法行善、也無法追尋到真理，換句話說，僅守法律是無法達到完美的境界。

The treatise on grace and law in Summa Theologica begins with the topic of practical philosophy before it talks further about the origin of theology, God. Therefore, Summa Theologica is not only a work of philosophy but also a masterpiece of theology. As for the treatise on law, his primary purpose is to deepen the concrete content of faith. And through discussing the multiple aspects of law, he explores its universal foundation-the eternal law. Aquinas' treatise on law covers the eternal law, the natural law, the human law, the law of the New Testament and the law of the Old Testament. Aquinas stresses over and over again: though law is important, neither can the good be done nor the truth be found, if human nature is not blessed with grace or one doesn't make good use of God's grace. In other words, the state of perfection can't be achieved through simply abiding law.