In this book there is a methodical analysis of everything concerning the Law of God and precisely: How necessary the Law of God is for man: how its revelation took place; which are the characteristics of the divine Law; how man acquires knowledge of it; the indispensability of obeying it. Finally, we examine which the usefulness of the divine Law is, especially in cases of sorrow. Moreover, several excuses - pretexts are stated, which are used by Christians of today, concerning the listening, knowledge and obedience of the divine Law and, at the same time, they are refuted.