Theological sources on sexual sin

Rob Banks

I was speaking to a friend I've known for years (not the friend who I referred to this forum, a different guy), and he was very resistant to my idea of sexual sin being bad (and to the idea of submitting to God and Truth at all).

I mentioned to him how a girl's physiognomy and spirit changes when she engages in casual sex (this is true for men too, although less so), but my friend insisted that casual sex is only bad for some people, but that others are able to enjoy it in moderation and not have it harm them spiritually.

Anyway, when I told him I could not explain exactly why and how casual sex changes a person's spirit for the worse but that there might be theologians and philosophers that can explain it better than I can, he asked me to send him some sources.

Does anyone know any good sources or writings by theologians about this topic? I thought someone like Thomas Aquinas might be a good source, but I'm not sure where to find his writings on the subject.

Tiger Man

You could, of course, point him to classical or ancient Doctors of the Church. But, for someone who is not theologically inclined, I would recommend going with something more recent. Cardinal Wojtyła (later Pope Saint John Paul II) wrote a book called Love and Responsibility that covers a lot of the "goods" of sexual purity/chastity and a lot of the "bads" of promiscuity and sexual sin. If you go a bit further back, you can get a copy of In Defense of Purity by Dietrich von Hildebrand. That is a lot more direct, and it covers far more of the contemporary issues we face than someone like Aquinas would.

Since you mentioned your friend is resistant to religion, I have to mention a potential secular source. Sexual Desire by Sir Roger Scruton reaches many of the same conclusions that a religious text would, but accomplishes it by way of secular reasoning. I have had some success in turning people to faith by first establishing an idea of natural law and order. Scruton's book may help in this way.

Rob Banks

↑For sure, thanks.

My friend isn't exactly the type to read an entire book, though. Maybe these sources are available online and there is a way to find relevant passages?
This is a great question. I found some really great Bible verses that can help explain why sexual sin is bad. The first verse is Hebrews 13:4 - "Let marriage be held in honor among all, and let the marriage bed be undefiled, for God will judge the sexually immoral and adulterous." This verse says that marriage should be undefiled. That means that we should save ourselves for marriage and stay faithful in marriage.

The next verse is 1 Corinthians 6:9,10, which says: "or do you not know that the unrighteous will not inherit the kingdom of God? Do not be deceived: neither the sexually immoral, nor idolaters, nor adulterers, nor men who practice homosexuality, nor thieves, nor the greedy, nor drunkards, nor revilers, nor swindlers will inherit the kingdom of God." This verse says that the sexually immoral will not inherit the kingdom of God. That means that sexual morality isn't just some small thing we maybe have to do, but it is something we NEED to do to enter the kingdom of God. That's a pretty big deal.

We all have sinned and we all aren't perfectly sexually moral. 1 Corinthians 10:13 says, "No temptation has overtaken you that is not common to man. God is faithful, and he will not let you be tempted beyond your ability, but with the temptation he will also provide the way of escape, that you may be able to endure it." This verse is amazing! It says that the temptations all of us face are common to every man. Also, it says that God won't let us be tempted so much that we cannot resist. This means that we can always resist the temptation no matter how hard because God is helping us.

The last verse I want to show you is 1 John 1:9, It says: "If we confess our sins, he is faithful and just to forgive us our sins and to cleanse us from all unrighteousness." This verse means that we can confess our sins to God and have them forgiven. God will cleanse us of our sins as long as we ask Him too. All of us have probably committed some kind of sexually immoral act, but that doesn't stop us from getting into Heaven. We need to realize what we have done is wrong and repent, then fight the temptations and grow. May God be with you, brother!


Gold Member
There are a few passages here, which come from several different sources and time periods.

Some short highlights below:

From St. John Cassions section on lust from On the Eight Vices is particularly good:

If we are really eager, as the Apostle puts it, to struggle lawfully and to be crowned (2 Tim: 2:5) for overcoming the impure spirit of unchastity, we should not trust in our own strength and ascetic practice, but in the help of our Master, God. No one ceases to be attacked by this demon until he truly believes that he will be healed and reach the heights of purity not through his own effort and labour, but through the aid and protection of God. For such a victory is beyond man's natural powers. Indeed, he who has trampled down the pleasures and provocations of the flesh is in a certain sense outside the body. Thus, no one can soar to this high and heavenly prize of holiness on his own wings and learn to imitate the angels, unless the grace of God leads him upwards from this earthly mire. No virtue makes flesh-bound man so like a spiritual angel as does self-restraint, for it enables those still living on earth to become, as the Apostle says, citizens of heaven (cf. Phil. 3:20).

And from a letter by St. Macarius of Optina, written in the 19th century:

"Yes," said Fr. Macarius with a sigh, "to you people of high society, such frivolity seems nothing, insignificant. But all the same, a terrible evil is hidden in it, causing an abyss of troubles and misfortunes and robbing your spiritual treasury. The Savior plainly says, Everyone who looks at a woman lustfully has already committed adultery with her in his heart (Matt. 5:28). You see—you only looked lustfully, and the sin has already been committed and the commandment of God broken. Even from a worldly point of view, how many bitter sorrows are caused by such predilections! Here, as I see it, you are now living happily and peacefully with your family. You love your wife and she loves you. You are candid with her, and have in her a friend who participates wholeheartedly in your sorrows and joys. But as soon as the thought of faithlessness enters your heart, the tempter will seize upon it right away and draw you with such strength that it will already be difficult for you to stop yourself and return to your sacred duty. From here it is not very far to a fall, and, if you commit it, everything is upset. In your wife, if she is faithful to you, you will have an enemy instead of a friend; you will begin to feel hatred towards her instead of love. instead of comfort, you will see in her a hindrance to the satisfaction of your crude and inhuman passion, and you will not even notice that you have become a lawless enemy to your lawful spouse. What a bitter future there is in such a life! But that is just here—what will happen beyond the grave? Terrible... It is a fearful thing to fall into the hands of the Living God" (Heb. 10:31).

And a few relevant Bible verses:

"For this is the will of God, your sanctification: that you should abstain from sexual immorality, that each of you should know how to possess his own vessel in sanctification and honor, not in passion of lust, like the Gentiles who do not know God." (1 Thess. 4:3-5)

"Beloved, I beg you as sojourners and pilgrims, abstain from fleshly lusts which war against the soul." (1 Peter 2:11)

"Let us walk properly, as in the day, not in revelry and drunkenness, not in lewdness and lust...But put on the Lord Jesus Christ, and make no provision for the flesh, to fulfill its lusts." (Romans 13:13-14)