418. What is the relationship between the natural law and the Old Law?The Old Law is the first stage of revealed Law. It expresses many truths naturally accessible to reason and which are thus affirmed and authenticated in the covenant of salvation. Its moral prescriptions, which are summed up in the Ten Commandments of the Decalogue, lay the foundations of the human vocation, prohibit what is contrary to the love of God and neighbor, and prescribe what is essential to it.
Further reading: CCC 1961-1962, 1980419. What place does the Old Law have in the plan of salvation?
The Old Law permitted one to know many truths which are accessible to reason, showed what must or must not be done, and, above all, like a wise tutor, prepared and disposed one for conversion and for the acceptance of the Gospel. However, while being holy, spiritual, and good, the Old Law was still imperfect because in itself it did not give the strength and the grace of the Spirit for its observance.
Further reading: CCC 1963-1964, 1982