The Sword in the Stone is technically a Sword in an Anvil on a Stone. Early swordsmiths would shape a weapon using a smoothed flat piece of stone, marble for preference. The term for one was a "sword-stone". When iron anvils began to take over, the term stuck around for a while. So the Sword in the Stone was thrust through two Sword-stones, the first a "modern" one of iron, tho other an old pagan one of stone. The Sword in the Anvil isn't as poetic as the Sword in the Stone, so the name stuck even though the language has moved on.
The Three Holy Kings in Christianity are neither holy nor kings, and we're not sure if there were three of them.
The belief that there were three of them comes from the verse in the Bible that says that "wise men" (who were likely astrologers) brought gifts of gold, frankincense, and myrrh. Three gifts, so it was assumed that there were three "kings".
At least some interpretations states that they pointed out that He was a king (gold), God (frankincense) and sacrificial Lamb (myrrh - which was used in burning rituals).
Speaking of the Bible, there are four books of John. The first one is called the book of John. The second is called First John, and so on. The explanation? John is technically the Gospel of John, while 1 through 3 John are The [X] Epistles of John.
Early Christianity had "Virgins of the Church," women who dedicated their time and money to helping the religious community. While celibate, they were actually more likely to be widows whose children were grown, since these women were more likely to be well-off and had few other responsibilities.
Heracles means "Glory of Hera". He's Zeus' son but not Hera's (he would be her nephew) and was given the name in an attempt to please her. It didn't work.
Although this may be because the myth of Heracles has been handed down to us in the Hera-phobic Theban version. It would appear that in the lost version from Argos, a city that took worship of Hera very seriously, the relationship between Heracles and Hera was portrayed on more friendly terms.
Another explanation: most of Heracles' greatest feats came from Hera's attempts to kill him, meaning that she is the unintentional source of his glory.
Epiphany (6 January), also called "Twelfth Night", is actually 13 days from Christmas Day (if both are included in the count). This is because the festive season, or "The Twelve Days of Christmas", traditionally began on Boxing Day. This confusion has in recent years caused some to erroneously identify January 5 as "Twelfth Night".