One could reasonably ask why Saint Valentine’s Day has romantic implications, as “saints” rarely have much, if anything, to do with romantic love.
One theory, which seems as good as any other, is that “The custom of sending Valentines on February 14 stems from a medieval belief that birds began to mate on that day”—this is courtesy of Delaney’s Dictionary of the Saints.
Another theory is that “the traditional association of St. Valentine’s Day with courtship and the choosing of a ‘Valentine’ is connected perhaps with certain customs of the pagan festival of Lupercalia (mid-February at Rome)”, this courtesy of Dr. E.L. Cross’s Oxford Dictionary of the Christian Church.
However, neither of the above explanations are particularly convincing, or edifying—let alone romantic.
Perhaps—and here we are on uncertain historical ground—the tradition arises from the fact that St. Valentine, as a priest (or possibly a bishop) was known for performing Christian marriages. At that time (the third century A.D.) this was against the Law of Rome and for performing these matrimonies, St. Valentine was placed under house-arrest.
Since he couldn’t go out and minister to his flock and exhort them, St. Valentine conspired to smuggle his sermons through his followers who were allowed to visit him.
These “love lessons” or “secret sermons” were the first known “Valentines” and as such were signed by him simply, “Valentine”.
What we are absolutely certain of is that, once St. Valentine became affiliated with the sharing of amorous missives, he was inextricably linked to that practice, regardless of its nebulous origin.
Happy Saint Valentine’s Day!