440. Why does the Decalogue enjoin serious obligations?

440. Why does the Decalogue enjoin serious obligations? 

(Comp 440) It does so because the Decalogue expresses the fundamental duties of man towards God and towards his neighbor.

“In brief”

(CCC 2081) The Ten Commandments, in their fundamental content, state grave obligations. However, obedience to these precepts also implies obligations in matter which is, in itself, light. 

To deepen and explain

(CCC 2072) Since they express man's fundamental duties towards God and towards his neighbor, the Ten Commandments reveal, in their primordial content, grave obligations. They are fundamentally immutable, and they oblige always and everywhere. No one can dispense from them. The Ten Commandments are engraved by God in the human heart. (CCC 2073) Obedience to the Commandments also implies obligations in matter which is, in itself, light. Thus abusive language is forbidden by the fifth commandment, but would be a grave offense only as a result of circumstances or the offender's intention.

Reflection

(CCC 1858) Grave matter is specified by the Ten Commandments, corresponding to the answer of Jesus to the rich young man: "Do not kill, Do not commit adultery, Do not steal, Do not bear false witness, Do not defraud, Honor your father and your mother"  (Mk 10:19). The gravity of sins is more or less great: murder is graver than theft. One must also take into account who is wronged: violence against parents is in itself graver than violence against a stranger. (CCC 1958) The natural law is immutable and permanent throughout the variations of history (Cf. GS 10) it subsists under the flux of ideas and customs and supports their progress. The rules that express it remain substantially valid. Even when it is rejected in its very principles, it cannot be destroyed or removed from the heart of man. It always rises again in the life of individuals and societies: Theft is surely punished by your law, O Lord, and by the law that is written in the human heart, the law that iniquity itself does not efface (St. Augustine, Conf. 2, 4, 9: PL 32, 678).    

(Next question: Is it possible to keep the Decalogue?)