How Do We Know the Moral Law?

Genesis 1:26-27 tells us that man is created in the image of God.  Many people fail to grasp how profound this revelation is.  Of all the thousands and thousands of creatures in the visible world, only man is made in the image and likeness of the all-knowing, all-loving, all-powerful, eternal God who created this awesome universe.  Unlike all other animals, we have spiritual souls; we have intellects and wills.  Like God, we can know and love (1).  We can receive God's own Spirit into our souls.  We are capable, one day, of living a life of unimaginable glory in heaven.

Because we are made in God's image (and thus have spiritual souls), we are truly free, unlike all other creatures in the visible world that are moved by instinct.  Because we are free, we are moral beings: we can choose to do either good or evil.  Through our intellect, we can discover the morality of goodness of an action.  This judgment of the intellect is called conscience.  Through our free will we can choose the good.  Or we can reject it and do evil.  

In making us in His image, God gives us a most precious gift.  However, with this gift comes accountability.  God commands us to use our free will to live according to the divine image.  We must be moral agents: doing what is good, avoiding what is evil.  If we do this, we will attain the final destiny, eternal glory in heaven, that God has planned for us:

Romans 2:5-10: For he will render to every man according to his works: to those who by patience in well-doing seek for glory and honor and immortality, he will give eternal life; but for those who are factious and do not obey the truth, but obey wickedness, there will be wrath and fury.  There will be tribulation and distress for every human being who does evil ... but glory and honor and peace for everyone who does good.

In heaven, we will possess the all-good God Himself; we will no longer be able to choose evil.  But in this earthly life, we can still sin and disfigure the divine image God gave us.  We can even lose the life of God in our souls through deadly (2) or mortal sin.

How do we know what is good and evil?  We consult the moral law, which is based on the eternal law of God.  Living according to the divine image means conforming to God's nature.  God is a God of truth, justice, and love.  Therefore, all our actions must be done in truth, justice, and love.  This is the essence of the moral law, which is not arbitrary or subject to chance by man.  The moral law is unchanging because God is unchanging: He will always be truth, justice, and love!  The moral law is our obligation to imitate God's eternal nature.

How do we know the demands of the moral law?  The Ten Commandments sum up the requirements of the moral law.  The two Greatest Commandments given by Jesus in Matthew 22:37-40 are a summary of the Ten Commandments:

Matthew 22:37-40: And he said to him, "You shall love the Lord your God with all your heart, and with all your soul, and with all your mind.  This is the great and first commandment.  And a second is like it, You shall love your neighbor as yourself.  On these two commandments depend all the law and the prophets."

We can also know the requirements of the moral law through human reason:

Romans 1:18-21: For what can be known about God is plain to them, because God has shown it to them.  Ever since the creation of the world his invisible nature, namely his eternal power and deity, has been clearly perceived in the things that have been made.

By examining ourselves, we obviously see we have a rational nature.  Our reason allows us to see the order God has put in the universe.  Our free will allows us to live according to that order.  Virtually all men agree that certain actions (honesty and faithfulness) are worthy of our rational nature; other actions (cheating and adultery) are unworthy.  This is known as the natural moral law.

The "natural law" is different from "law of nature."  Man is certainly subject to "laws of nature" such as gravity.  But reason discerns that man is also accountable to a higher law, a "law of human nature."  We don't blame rocks or animals for hurting us, because they aren't rational and can't act differently.  However, we do blame a man for deliberately hurting us, because humans are rational and obviously can act differently, and because of that, should.

However, because of original sin, our reason is wounded.  Thus, our understanding of the moral law through reason alone is subject to error.  Happily, God gave Moses the Ten Commandments on Mount Sinai.  Through public revelation, then, we know the requirements of the moral law without error.

The Catholic Church, which teaches with the authority of her founder Jesus Christ (3), is the final and infallible interpreter of both the natural moral law and public revelation.  Thus, she is a reliable teacher when it comes to the life issues.


(1) - Obviously, the way we know and love will be conditioned by our nature.  God knows and loves infinitely, because He is infinite.  We know and love finitely, because we are finite.  However, there is still a real analogy, a real likeness, between God's ability to know and love and our own.

(2) - 1 John 5:16-17

(3) - Luke 10:16, Matthew 28:18-20, We presume the reader recognizes that the Catholic Church is the original and true Christian Church.  In addition to her unbroken historical continuity from the time of Christ and the Apostles, she has also preserved an unbroken doctrinal continuity (as evidenced by the beliefs of the early Church Fathers) as well as an unbroken continuity of apostolic teaching authority (in her bishops and popes, ordained successors to the Apostles).  We direct the unconvinced to our earlier booklets and the undeniable historical record.


Included in this booklet:



How Do We Know the Moral Law (included above)
How Do We Evaluate Moral Acts?
Approved Moral Principles
False Moral Ideas

Church Teaching on Abortion
Answering the "Top 12" Pro-Abortion Arguments

Church Teaching on Euthanasia
Answering Euthanasia Supporters

Methods of Contraception
Church Teaching on Contraception
Answering Objections to the Church's Teaching

Same-Sex Unions

Artificial Procreation (Test-Tube Babies)
Artificial Insemination

What is Allowed Outside Marriage?
What is Allowed Within Marriage?
What if My Pastor Says Contraception or Sterilization is OK?
What if My Spouse Keeps Contracepting?
What if I Have Been Sterilized?

Father Frank Chacon, and Jim Burnham. Beginning Apologetics 5: How to Answer Tough Moral Questions: Abortion, Contraception, Euthanasia, Test-Tube Babies, Cloning & Sexual Ethics. Farmington, NM: San Juan Catholic Seminars, 2000-2015. Print.

To order one or more of the Beginning Apologetics books by Father Frank Chacon and Jim Burnham, see San Juan Catholic Seminars' website.