Valentine's Day (that'd be today, and yes, it's too late to try and order roses you loser) was originally the Roman feast of Lupercalia, a celebration of fertility. Around the year 270 AD the holiday was Christianized (for whiter whites try Christianity!) and the date changed from February 15 to 14 to commemorate the martyred Saint Valentine. By the late Middle Ages, the modern tradition of exchanging paper love declarations evolved.
So, what they're saying is that the Christian Church went and took yet ANOTHER pagan feast day and made it their own by a little smoke, some mirrors, and a fast sleight of hand. And I thought the Romans were bad.