Natural Law is not all that man needs to attain his end; he also needs positive law, and for many reasons. Man's intellect may err in applying principles. It may be misled by custom, inclination, or surroundings. Also, the well-being of men in general necessitates positive law to determine and govern rights and duties of individuals to promote the common good of all. Furthermore, man's circumstances change, and his course amid new and changing circumstances is sometimes insufficiently indicated by the Natural Law. Positive law will direct him amid all changing circumstances. This positive direction may come from God or from man. Thus, man has, besides Natural Law, positive law, both divine and human, to enable him to reach his end.
The principal reason for man's need of revealed Positive Law from God is that Man's destiny is a supernatural destiny, concerning which the Natural Law is silent, for the supernatural law is above human nature. The Natural Law is incomplete and insufficient man's end. Man needs, therefore, from God a revealed positive statement of the law by which his destiny is to be attained.
From the beginning, man has had the Divine Positive Law of life and destiny before him. When God made our first parents, He revealed to them the law by which they would reach their supernatural destiny. He promulgated positive laws regarding man's conduct to his Creator, his neighbor, and himself, as is clearly indicated in the Book of Genesis. To Moses, also, God gave the Commandments, which were a more abundant and emphatic promulgation of man's duties as already contained in the Natural Law, of which many had lost sight.
When God the Son became man, He promulgated a new law by which men were to make the journey of life and reach their supernatural destiny. Jesus Christ took the Ten Commandments and summed them up into two: "Thou shalt love the Lord thy God with thy whole heart," and "Thou shalt love thy neighbor as thyself." On these two Commandments, the whole law is based. Love, then, is the source of all law; and that law is love. He also taught that mere external observance of the law (as shown by the Pharisees) was not enough, and He emphasized internal obedience to the law. The root of action is mind or heart, and sins of thought or desire are as serious as sinful actions. Christ further revealed a whole body of detailed laws or rules whereby the love of God and of our neighbor are to be shown. This body of rules or laws Christ entrusted to His Church, from whom alone can men learn what is contained therein. Christ established His Church for one purpose only - namely, to teach men infallibly the truths of life's meaning and purpose, and guide them unerringly to their final destiny. Men are obliged to accept the Law of Christ as taught by His Church, because the Church is the sole authorized and divinely-appointed guide for all men, for all time, in the way of salvation.
To the Catholic Church belongs the right to say what is contained in the Natural Law. She is the divinely-appointed custodian, interpreter, and promulgator of Divine Positive Law. And while the Church cannot alter God's Law, whether it be the Natural Law or Divine Positive Law, she can, within the framework of God's Law, make bylaws with His authority; e.g., she requires the presence of a Priest for Catholic Marriage. These bylaws, being her own, she can alter, but she cannot alter God's Law, nor has she any desire to do so.
The New Law which God gave to the Church covers all the duties that arise from man's relations with God, himself, and other men in the supernatural order: to God the Father, as a son; to God the Son, as a member of His body, i.e., the Church; to God the Holy Ghost, as the temple in which He dwells; to himself, as subject in all his faculties by grace to God; to other men, as co-heirs of the same kingdom in the brotherhood of sons of a common Father Who is in heaven.
The New Law promulgated by the Church with God's authority imposes on all men an obligation to work to obtain their supernatural destiny: "With fear and trembling work out your salvation." (Phil. 2:12) Man must, first, acknowledge God, in theory and in practice, as his ultimate end, i.e. he must reject everything that makes that end impossible - that is, he must avoid sin. He must believe in God, hope in Him, and love Him. Man must also work positively - that is, do good: firstly, he must receive Baptism. "Unless a man be born again of water and the Holy Ghost, he cannot enter the kingdom of heaven." (John 3:5) Secondly, he must observe the Commandments. "If thou wilt enter into life, keep the Commandments." (Matt. 19:17) Thirdly, he is bound to regain by Penance his claim to his last end should he lose it through sin.
The Church does not, however, displace man's conscience; rather, by her teaching, the Church renders man's conscience properly instructed, and gives him a clear perception of the law and its obligations, enabling him to follow his conscience unswervingly. God has given a sanction with His Laws: the reward of heaven for all those who observe them, and the punishment of hell for all those who break them. God has made this sanction so clear to men that any doubt on the matter is impossible.
All men are called to perfection by Jesus Christ Himself - "Be ye therefore perfect" (Matt. 5:48) - and they have in Him the ideal to which they should aspire. The only type of goodness in the present order is Christian goodness. The only ideal of perfection in the present order is the Christian ideal: Jesus Christ. He came to show men the way to heaven by example as well as teaching. The domestic society of the family and the civil society of their fellow men will assist men to attain perfection and their last end, but Jesus Christ alone is the Leader and Master in the way of perfection. He commands men: "Follow Me, I am the way, the truth, and the life." He gave men not only divine commands, but also divine counsels. By cooperation with the divine aid, all men of goodwill can attain moral perfection, as shown in their model, Jesus Christ. To this perfection men are obliged to rise and acquire the essential resemblance to Christ, who, being God, for man's sake became man.
62. Is the Natural Law all that man needs to attain his end?
No. Man needs positive law also.
63. What is the principal reason for man's need of revealed Positive Law from God?
The principal reason is this: Man's destiny is a supernatural destiny, concerning which the Natural Law is silent. Man needs, therefore, a statement from God of the laws of supernatural life and purpose.
64. Has God always provided the human race with the Divine Positive Law which is necessary if men are to attain their supernatural destiny?
Yes. From the beginning, man has had the Divine Positive Law of life and destiny before him.
65. When God the Son became man, did He give any New Law to men?
Yes. Jesus Christ promulgated a New Law by which men were to make the journey of life and reach their supernatural destiny.
66. If men wish to attain their supernatural destiny, must they accept the Law of Christ as taught by His Church?
Yes, that is God's arrangement, which all men are obliged to accept.
67. What is the scope of the Church's power with regard to God's Laws?
The Church is the interpreter of the Natural Law; she is the interpreter and promulgator of the Divine Positive Law; and she is empowered to make laws of her own.
68. Does the New Law which Christ gave to His Church contain all the guidance that man needs for the supernatural life?
Yes. The New Law which God gave to the Church covers all the duties that arise from man's relations with God, himself, and other men in the supernatural order.
69. What are men obliged to do by the New Law which God promulgates through the Church?
The New Law promulgated by the Church with God's authority imposes on all men an obligation to work to obtain their supernatural destiny.
70. What is comprised in this fundamental obligation on man to work towards the realization of his last end?
Man must both acknowledge God in theory and in practice as his ultimate end, and work positively - that is, do good.
71. Does the Church, then, displace man's conscience?
No. Man's conscience is not displaced by the Church; by her teaching, the Church renders his conscience properly instructed, and gives man a clear perception of the law and its obligations, enabling him to follow his conscience unswervingly.
72. Had God given any sanction to His Laws?
God has given a sanction with His Laws: the reward of heaven for all those who observe them, and the punishment of hell for all those who break them.
73. Are all men called to perfection, and have they an ideal of perfection to which they should aspire?
Yes. Man, by the Natural Law, is obliged to attain perfection, and the ideal to which they should aspire is that of Jesus Christ Himself.