The astounding popularity of J.R.R. Tolkien and his writings–magnified many times over by the success of the Lord of the Rings films–has ensured that Tolkien’s fantasy world of moral meaning stands as one of the great literary achievements of our times.

In some sense, Tolkien was a man born out of time. A philologist at heart, Tolkien was most at home in the world of ancient ages, even as he witnessed the barbarism and horrors of the 20th century. Celebrated as a popular author, he was an eloquent witness to permanent truths. His popularity on university campuses, extending from his own day right up to the present, is a powerful indication of the fact that Tolkien’s writings reach the hearts of the young, and those looking for answers.

Even as Tolkien is celebrated as an author and literary figure, some of his most important messages were communicated by means of letters, and some of the most important letters were written to his sons.

Tolkien married his wife Edith in 1916, and the marriage was blessed with four children. Of the four, three were boys. John was born in 1917, Michael in 1920, and Christopher in 1924. Priscilla, the Tolkiens’ only daughter, was born in 1929.

Tolkien dearly loved his children, and he left a literary legacy in the form of letters. Many of these letters were written to his sons, and these letters represent, not only a hallmark of literary quality, but a treasure of Christian teaching on matters of manhood, marriage, and sex. Taken together, these letters constitute a priceless legacy, not only to the Tolkien boys, but to all those with whom the letters have been shared.

In 1941, Tolkien wrote a masterful letter to his son Michael, dealing with marriage and the realities of human sexuality. The letter reflects Tolkien’s Christian worldview and his deep love for his sons, and at the same time, also acknowledges the powerful dangers inherent in unbridled sexuality.

“This is a fallen world,” Tolkien chided. “The dislocation of sex-instinct is one of the chief symptoms of the Fall. The world has been ‘going to the bad’ all down the ages. The various social forms shift, and each new mode has its special dangers: but the ‘hard spirit of concupiscence’ has walked down every street, and sat leering in every house, since Adam fell.” This acknowledgement of human sin and the inevitable results of the Fall stands in stark contrast to the humanistic optimism that was shared by so many throughout the 20th century. Even when the horrors of two world wars, the Holocaust, and various other evils chastened the century’s dawning optimism of human progress, the 20th century gave evidence of an unshakable faith in sex and its liberating power. Tolkien would have none of this.

“The devil is endlessly ingenious, and sex is his favorite subject,” Tolkien insisted. “He is as good every bit at catching you through generous romantic or tender motives, as through baser or more animal ones.” Thus, Tolkien advised his young son, then 21, that the sexual fantasies of the 20th century were demonic lies, intended to ensnare human beings. Sex was a trap, Tolkien warned, because human beings are capable of almost infinite rationalization in terms of sexual motives. Romantic love is not sufficient as a justification for sex, Tolkien understood.

Taking the point further, Tolkien warned his son that “friendship” between a young man and a young woman, supposedly free from sexual desire, would not remain untroubled by sexual attraction for long. At least one of the partners is almost certain to be inflamed with sexual passion, Tolkien advised. This is especially true among the young, for Tolkien believed that such friendships might be possible later in life, “when sex cools down.”