We often hear the argument today: “What two people do together voluntarily is not a sin. If no one is harmed, it’s purely a private matter.” But this view is a fatal error that misunderstands the meaning of our existence. For sin is not simply an arbitrary prohibition by God to spoil our fun. Sin means acting against our own good and against the order that God has placed in our nature.
God did not create the sexual act as a mere plaything, but as the sacred way to pass on life. The seed of man is not like sweat or another excretion that is meaningless. It carries the potential of an immortal human being within it. Whoever uses this power must also take responsibility for its purpose: the child. And God’s creation shows us clearly: To conceive a child is pointless if one is not prepared to raise it as well.
What Creation Teaches Us (The Example of Nature)
If we look at the animal world, we see God’s wisdom. In animals where the mother alone can care for the young (as in dogs, who nurse their puppies), male and female separate again. But consider birds: a female bird cannot sit on the eggs to keep them warm and fetch food at the same time. If the male were to fly away, the brood would die. That is why the Creator has placed in their nature the necessity to stay together. This is not a romantic decision, but a necessity of life.
Humans Need More Than Just Food.
If even birds by nature need a stable bond, how much more so humans? The human child is the most needy creature in creation. It needs not only years of physical care. As a being with an immortal soul, the child above all needs “food for the spirit”: upbringing, education, learning virtue, and the way to God. This is a lifelong task that takes decades. Leaving a mother alone with this contradicts justice and nature.
God created humans so that the child needs the constant guidance of both father and mother—the father for protection and authority, the mother for care and security. This necessary, lifelong community is what we call marriage.
Why Fornication Is a Grave Sin.
Therefore, every sexual act outside of marriage is a serious offense against God and life. Those who engage in “simple fornication” want pleasure, but deny possible life the protected space (marriage) it absolutely needs. They act against love and against responsibility for the next generation. Marriage is thus not merely a law of the Church, but a commandment of reason and of nature itself. True love takes responsibility—everything else is selfishness.
Even if a wealthy woman could support a child on her own, the act remains wrong. Moral laws are based on what is generally good for human nature, not on rare exceptions.
For Further Study
Thomas Aquinas, Summa contra Gentiles / Sum Against the Gentiles, Book 3, Chapter 122