The beginning of Valentine's Day is connected to stories about the early Christian saint and martyr, St. Valentine. Accounts differ, but in the 4th century it is said there was a godly Christian named Valentine who was imprisoned for his faith under the Roman Emperor Claudius II.
The Emperor tried to get Claudius to convert to paganism, and Valentine tried to convert the Emperor to Christianity. In the process, it is said that the jailer turned to Christ and God used Valentine to heal the jailer's daughter of blindness. Valentine was then sentenced to death and executed. One legend has it that one of his last acts was to send a card signed "Your Valentine" to the jailer's daughter who could now see.
St. Valentine's Day has been celebrated by Christians for centuries. Then in the 1300's, the day became associated with romantic love by the poet Chaucer, and that tradition has continued to this day.
And now you know the rest of the story!